Proc. Natl. Acad. Sci. USA Vol. 76, No. 2, pp. 920-924, February 1979 Immunology Regulation of immune response to tumor : Interference with syngeneic tumor immunity by anti-IA alloantisera (tumor growth/I region/H-2 complex) LINDA L. PERRY, MARTIN E. DORF, BARUJ BENACERRAF, AND MARK I. GREENE Department of Pathology, Harvard Medical School, 25 Shattuck Street, Boston, Massachusetts 02115 Contributed by Baruj Benacerraf, November 28, 1978

ABSTRACT We present evidence for a role of I-A subre- immune interactions among T cells, B cells, and macrophages gion-encoded determinants in syngeneic tumor immunity. In (21). It will be shown herein that the in vivo administration of animals rendered immune to the S1509a fibrosarcoma, daily antisera directed against products coded by the I-A subregion treatment with microliter quantities of antisera directed against effectively limits the capacity for immune tumor rejection in Kk and I-Ak determinants expressed on lymphoid cells of host a secondary response. Furthermore, immune animals pre- origin decreased the capacity for immune tumor rejection. Absorption studies revealed that anti-I-Ak antibody activity treated with such an anti-I-A antiserum can no longer adop- alone was sufficient for the manifestation of this effect. Fur- tively transfer effective tumor immunity to naive syngeneic thermore, experiments utilizing F1 hybrids showed that an an- recipients. tiserum that was genetically unable to interact with H-2 deter- minants expressed on the tumor was equally effective in in- hibiting tumor immunity. Suggestive evidence that the activity MATERIALS AND METHODS of this antiserum is related to interference with the generation of effector T function was provided by the observation that Mice. A/J (H-2a) and (BALB/c X A/J)F1 (H-2d/a) female hyperimmune animals pretreated with an anti-KkI-Ak antise- mice 8-10 weeks of age were obtained from The Jackson rum were no longer capable of adoptively transferring tumor Laboratory. immunity to naive recipients. Thus, it is possible to regulate the Tumor. The S1509a tumor, a MCA-induced fibrosarcoma secondary immune response to tumor by using antisera in A/J mice, was maintained both in vitro and in vivo by with specificity for I-A determinants expressed on cells or pos- transfer of ascitic fluid obtained from the peritoneal cavity of sibly on factors of the host lymphoid system. mice given 105-106 sarcoma cells. Culture conditions have been Syngeneic carcinogen-induced tumors have been shown to be described (17). immunogenic in mice (1-3), although the cellular events Antisera. The antisera used in these experiments included underlying efficient tumor rejection are still incompletely (C57BL/10 X LP.RIII)Fl anti-BlO.A(4R) cells (anti- understood. Whereas it is apparent that T cells, (4-8) macro- Kk,I-Ak) and (A/J X C57BL/10)Fl anti-B1O.GD(N4) spleen phages (4, 9), B cells (10), and other cell types as well (11-14) cells (anti-Kd,I-Ad). The cytolytic titers of these sera were 1:1024 all may participate in the immune response to tumor antigens, and 1:512, respectively. A C3H anti-C57BL/6 antiserum (titer the role of T cells in this response is critical. First, cytolytic T 1:320) was also used in one experiment. Normal A/J serum was cells have been shown to possess the capacity for tumor cell lysis used as a control. In all experiments, mice received daily in- in vitro and in vivo (5-7); second, suppressor T cells capable travenous injections of 0.2 ml of isotonic saline containing 2-10 of limiting effector response have been characterized in Ml of serum. Sera were absorbed twice at 4°C with 1 spleen vivo (15) and in vitro (16). equivalent of lymphocytes or with 108 S1509a ascites cells per These suppressor T cells have been found predominantly in ml of antiserum in certain experiments. the and spleen of animals bearing primary methyl- Procedure for Immunization. For immunization with the cholanthrene (MCA)-induced tumors (17, 18). Previous reports S1509a tumor, A/J mice received 105-106 cells subcutaneously from this laboratory have further demonstrated the suscepti- in the back. Tumors were surgically removed 1 week later. Such bility of tumor-specific suppressor cells to modulation by an- mice are regarded as immune, as evidenced by their rejection tisera directed against determinants encoded by the I-J sub- of a subsequent tumor challenge. Hyperimmune mice were region of the H-2 complex (15). Mice treated with this antise- prepared by several subsequent injections of live tumor cells rum in vivo exhibit an augmented immune responsiveness to into immune mice as described (17). Animals treated in this tumor antigen that is manifested as decreased tumor growth manner consistently can reject a 106-cell inoculum of S1509a and enhanced tumor cell destruction (19). The target of anti- within 14 days. body treatment may be either the I-J (+) suppressor cell or the Adoptive Transfer of Immunity. S1509a hyperimmune A/J I-J determinant-bearing suppressor factor elaborated by these mice, boosted with 105-106 S1509a cells 9-10 days previously, cells (20). were given 10 Al of anti-Kk,I-Ak antiserum daily (or Hanks' We have now investigated the effect of treatment with an- solution in the case of controls) intravenously for 5 days. tisera produced to interact with K- and I-A-encoded major and draining lymph nodes were removed on day 6, and the cells histocompatibility complex (MHC) determinants on the ex- were separated in serum-free Eagle's minimal essential medium pression of immunity to MCA-induced tumors. These experi- (Microbiological Associates, Walkersville, MD) by using glass ments were initiated on the basis of the growing body of evi- grinders. Cell suspensions were washed three times in this dence implicating a role for the I-A subregion in regulating medium and resuspended to 2.5 X 108 cells per ml. A sample (0.2 ml) of this suspension was injected intravenously into The publication costs of this article were defrayed in part by page normal A/J recipients at the time of tumor challenge. charge payment. This article must therefore be hereby marked "ad- vertisement" in accordance with 18 U. S. C. §1734 solely to indicate Abbreviations: MCA, methylcholanthrene; MHC, major histocom- this fact. patibility complex. 920 Downloaded by guest on September 28, 2021 Immunology: Perry et al. Proc. Natl. Acad. Sci. USA 76 (1979) 921 In Vivo Measurement of Tumors. The growth of S1509a serum or an irrelevant C3H anti-C57BL/6 (anti-H-2b) serum in vivo was determined by measuring the perpendicular di- had no discernible effect (data not shown). It should be noted ameters of the tumor with vernier calipers. Surface area was that it was essential to continue administration of anti-Kk,I-Ak previously shown to corroborate precisely with both tumor antiserum to demonstrate enhanced tumor growth, and ter- weight (22) and histologic differences seen between groups (17, mination of administration was followed by rapid tumor re- 18). jection. Statistical Analysis. The statistical significance of results Specificity of (C57BL/10 X LP.RIII)F1 Anti-B1O.A(4R) obtained by tumor measurements of groups consisting of five Alloantiserum. In order to establish that the anti-Kk,I-Ak an- or more animals was calculated by Student's t test as computed tiserum mediated this effect by a capacity to interact with by the Wang programmable computer. Arithmetic means products coded for by the H-2 complex, the serum was ab- (±SEM) are indicated in the figures. sorbed with 4 X 108 B1O.BR (H-2k) lymphocytes or an equal Cytotoxicity Testing. Lymphocytotoxicity assays were number of C57BL/10 Sn (H-2b) lymphocytes. The capacity performed as described (23). of the serum to inhibit tumor immunity was lost after absorption with lymphocytes of the H-2 relevant B1O.BR strain whereas RESULTS serum absorbed with control cells of the H-2b haplotype showed Effect of Alloantisera Directed to Products of K and I-A no loss of activity and was still capable of effecting the rejection Regions on Secondary Tumor Immunity. Preliminary ex- of the tumor (Fig. 2). Furthermore, animals treated with this periments were performed to determine the effect of in vivo latter serum or with unabsorbed anti-KkI-Ak antiserum dis- administration of antiserum directed to products of the Kk and played a significant mortality rate (60%) as a result of fatal I-Ak regions of the murine MHC (24). It was found that daily tumor escape, whereas animals that received the B1O.BR ab- administration of 10 Al of such an antiserum to animals ren- sorbed serum or control normal mouse serum exhibited com- dered hyperimmune to the S1509a fibrosarcoma resulted in plete tumor elimination within 15 days and were thereafter augmented tumor growth upon tumor rechallenge compared tumor-free with 0% mortality. Thus, it can be inferred from to untreated controls. To define this effect further, we studied these results that the ability of anti-Kk,IAk antiserum to in- the ability of antiserum treatment to interfere with tumor re- terfere with immune tumor rejection relates to its capacity to jection in animals less highly immune to the S1509a tumor and, interact with antigenic determinants expressed on H-2k spleen therefore, more susceptible to immune modulation. Normal cells. A/J mice were given 106 S1509a cells subcutaneously and the Anti-I-Ak Antiserum Inhibits Tumor Rejection. In an at- resultant tumor was surgically removed 7 days later. After a tempt to establish more precisely the specificity of this serum period of 14-21 days, these animals were rechallenged with 106 for determinants encoded by the MHC, the following series of S1509a cells. As seen in Fig. 1, and as shown previously (17), these animals could consistently reject a secondary challenge within 14 days. However, the daily administration of 10 Al of (C57BL/10 X LP.RIII)F1 anti-BlO.A(4R) alloantiserum (re- ferred to as anti-Kk,I-Ak antiserum), beginning at the time of tumor rechallenge, resulted in an inhibition of tumor rejection compared to controls. The administration of normal mouse

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Time, days FIG. 2. Specificity of (C57BL/6 X LP.RIII)F1 antiBlO.A(4R) 0 2 4 6 8 alloantisera. The specificity of anti-Kk,I-Ak antisera for determinants Time, days encoded by the H-2 complex was determined by absorption with FIG. 1. Inhibition of immune tumor rejection by using antisera spleen cells of the B1O.BR (H-2k) and BlO (H-2b) congenic strains. directed against Kk and I-Ak region determinants. Aid mice, rendered S1509a immune AiM mice, challenged with 105 S1509a cells subcu- immune to the S1509a tumor by previous immunization followed by taneously, were given daily intravenous injections of 10 ,ul of anti- surgical tumor removal, were rechallenged with 106 S1509a cells Kk,I-Ak antisera that was either unabsorbed (U) or absorbed with subcutaneously. These animals were given daily intravenous injections H-2k (A) or H-2b (0) splenocytes. Normal mouse serum was used as of 10 gl of a (C57BL/6 X LP.RIII)F1 anti B1O.A(4R), anti-Kk,I-Ak a control (s). Antiserum activity was no longer apparent after ab- antiserum (0) or Hanks' solution (0) as a control, beginning at the sorption with the B1O.BR (H-2k) cells. Data are shown as mean + time of tumor rechallenge. Data are shown as mean ± SEM. SEM. Downloaded by guest on September 28, 2021 922 Immunology: Perry et al. Proc. Natl. Acad. Sci. USA 76 (1979) experiments was performed. The anti-KkI-Ak antiserum was depleted of antibody activity directed toward the Kk deter- minants by absorption with 108 S1509a tumor cells. These cells express both K and D region determinants but bear no de- tectable I region specificities. After absorption, anti-Kk activity was no longer apparent, whereas the anti-I-Ak titer (1:320) of E the serum was undiminished as determined by cytotoxicity N against A.TL spleen cells. Administration of this absorbed serum ._A to immune animals at doses of 2 Al/day resulted in a degree of To immune interference similar to that observed with unabsorbed E o.- anti-Kk,I-Ak antiserum (Fig. 3). Thus, an antiserum with the capacity to interact only with I-A determinants can limit the generation and manifestation of tumor immunity. In addition, these results argue against a spurious effect of antibody on the tumor itself. The exclusive role of antibody directed against I-Ak deter- minants in the abrogation of secondary tumor immunity was Time, days substantiated by performing the reverse experiment as follows. X FIG. 4. Loss of the ability to inhibit tumor immunity by depletion (C57BL/10 LP.RIII)F1 anti-BIO.A(4R) anti-Kk,I-Ak antise- of anti-I-Ak antibody activity. (C57BL/10 X LP.RIII)F1 anti- rum was depleted of anti-I-Ak activity by absorption with spleen BlO.A(4R) anti-Kk,I-Ak was absorbed with splenocytes of the A.TL cells of the A.TL(H-2tl) strain. Cytotoxicity tests using the ab- strain to remove anti-I-Ak antibody activity without diminishing sorbed sera demonstrated that the serum still had a cytolytic anti-Kk antibody activity. Administration of 2 pl/day of A.TL-ab- titer of 1:320 with H-2k cells. Control absorptions using sple- sorbed antiserum to S1509a immune A/J had no disruptive effect on nocytes of the C57BL/6(H-2b) strain were also performed. As the rejection of a 105 S1509a challenge (0); treatment with control in possessing anti-K C57BL/6 absorbed (0) or unabsorbed anti-Kk,I-Ak antisera (0) re- shown Fig. 4, antiserum but lacking sulted in significant inhibition of immune tumor rejection as com- anti-I-Ak activity was no longer capable of inhibiting tumor pared to animals treated with Hanks' solution (M). rejection, whereas the administration of control absorbed or unabsorbed antiserum resulted in significantly enhanced tumor growth compared to untreated animals. Results of these two interacting with I-A determinants has the capacity to interfere absorption experiments argue strongly against any possibility with the cellular events leading to efficient immune tumor that irrelevant antibody specificities may be responsible for the rejection in vivo. observed effects and provide convincing evidence that antibody Effect of Anti-Kd,I-Ad Antiserum on S1509a Tumor Growth in (BALB/c X A/J)F1. Further evidence for an interaction between anti-I-A antibodies and determinants expressed on cells of host rather than of tumor origin was obtained in the following manner. An antiserum directed against the K and I-A antigens of the H-2d haplotype was administered at doses of 4 gl/day to previously immunized (BALB/c X A/J) (H-2d/a)FI hybrids rechallenged with the H-2a S1509a sarcoma. This particular antiserum, prepared in an (A/J X C57BL/10)Fl host, was in- capable of interaction with H-2a determinants present on host lymphoid or tumor tissues yet could still react with the Kd and I-Ad antigens expressed by the (BALB/c X.A/J)Fl host. Results of a representative experiment are presented in Fig. 5. It is clear from these data that treatment with an anti-Kd,I-Ad antiserum which has the capacity to interact with cell surface determinants encoded by only one of the parental haplotypes and not with antigens expressed on the tumor is still capable of effectively limiting host immunity in the secondary response to the tumor. Effect of Anti-KkI-Ak Antiserum on Transferable Tumor Immunity. It had previously been established that a certain level of immunity to the S1509a tumor could be achieved in normal animals in vivo by the adoptive transfer of lymphocytes from hyperimmunized donors (unpublished data). The effector Time, days cells responsible for tumor destruction have been shown to be of T lineage by their sensitivity to treatment with anti-Thy 1.2 FIG. 3. Anti-I-Ak antibody activity is sufficient to inhibit tumor immunity. (C57BL/10 X LP.RIII)F1 anti-BlO.A(4R) anti-Kk, I-Ak and complement in vitro (M. Greene, unpublished data) prior alloantiserum was absorbed with 108 S1509a tumor cells. The ab- to adoptive transfer of tumor immunity to naive recipients, in sorbed serum was depleted of anti-Kk activity but the anti-I-Ak titer agreement with other reports on effector mechanisms in this was undiminished. Daily intravenous administration of 2 ,l of either system (25). It therefore was of interest to determine whether absorbed (0) or unabsorbed (3) antiserum resulted in the inhibition donor animals pretreated with an anti-Kk,I-Ak antiserum of tumor rejection in immune A/J mice given 105 S1509a cells sub- maintained the ability to transfer effective tumor immunity cutaneously compared to controls treated with Hanks' solution (0). These results also demonstrate the lack ofspecificity of this antiserum to naive recipients. for determinants on the S1059a tumor. Data are shown as mean i Preliminary investigations designed to optimize conditions SEM. for an efficient transfer resulted in the following protocol. A/J Downloaded by guest on September 28, 2021 Immunology: Perry et al. Proc. Natl. Acad. Sci. USA 76 (1979) 923

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0 2 4 6 8 10 Time, days 0.1 < 0.005 FIG. 5. Anti-Kd,I-Ad antiserum inhibits S1509a rejection in im- mune (BALB/c X A/J)F1 hosts. (C57BL/10 X A/J)F1 anti-B1O.GD (anti-Kd, I-Ad) alloantiserum was injected intravenously, daily, into (BALB/c X A/J)F1 immune hosts beginning at the time of a 106 0 2 4 6 8 10 S1509a cell challenge (0). Hanks' solution was used in lieu of anti- Time, days serum in control animals (0). This antiserum was unable to interact with H-2a determinants expressed on the tumor because it was pro- FIG. 6. Treatment with anti-Kk,I-Ak antiserum abrogates the duced in H-2d/H-2a F1 hybrids. ability to transfer tumor immunity. S1509a hyperimmune A/J mice were boosted with lo' S1509a cells and 9 days later were treated (10 mice, hyperimmunized to the S1509a sarcoma, were challenged gl/day) with (C57BL/10 X LP.RIII)F1 anti-BlO.A(4R) anti-Kk,I-Ak alloantiserum (3) or normal mouse serum (0) for 5 consecutive days. with 105-106 tumor cells and then, 9-10 days later, were treated On day 6, 5 X 107 cells obtained from the spleen and draining lymph (10 til/day) with either anti-Kk,I-Ak antiserum or normal mouse nodes were adoptively transferred to normal A/J mice which were serum for 5 consecutive days. At the end of this time, 5 X 107 simultaneously immunized with 5 X 105 S1509a cells subcutaneously. cells obtained from the spleens and draining lymph nodes of Donors pretreated with anti-Kk,I-Ak antiserum were no longer capable these animals were adoptively transferred to normal recipients, of transferring tumor immunity when compared to normal animals which were simultaneously challenged with 5 X 105 S1509a not receiving cells (@). P values refer to the comparison of tumor size in naive animals receiving cells from normal mouse serum-treated cells subcutaneously. As shown in Fig. 6, normal animals re- immune animals to tumor size when naive mice received cells from ceiving cells from donors treated with normal mouse serum S1509a immune mice pretreated with anti-KkI-Ak serum. displayed significantly reduced tumor growth as compared to animals not receiving cells. Pretreatment of donor animals with administration daily of 5 Al of a C57BL/6 anti-AD755a anti- anti-Kk,I-Ak antisera, however, abolished their ability to provide serum containing known anti-gp7l activity (26) had no en- protection to recipient hosts. These results imply that mice hancing or inhibitory effects on growth of the S1509a tumor treated with anti-Kk,I-Ak antiserum no longer constitute a in normal A/J hosts (data not shown). Collectively, these results source of immune effector cells to the S1509a tumor. obviate any potential for direct interactions between antibody and the tumor itself-first, because the antiserum used in cer- DISCUSSION tain of these experiments was absorbed with the Ia(-) S1509a The experiments documented herein provide unequivocal tumor prior to testing, and second, because antiviral antibody demonstration that I-A subregion-encoded determinants play does not appear to affect tumor development in this system. a significant role in syngeneic tumor immunity. We have Further support for this concept was obtained from results demonstrated that in vvo treatment of immune mice with of experiments utilizing F1 hybrids and an anti-K,I-A antiserum microliter amounts of anti-Kk,I-Ak antiserum decreased their having the potential to interact with determinants encoded by capacity to reject syngeneic tumor grafts to which they were only one parental haplotype and not with the tumor used for immune. Furthermore, recent experiments have similarly challenge. Again, antiserum treatment diminished the capacity shown that anti-Kk,I-Ak antiserum administration limits the of the F1 host to mediate efficient tumor rejection. These data development of delayed type hypersensitivity to tumor antigen thus substantiate the absence of any spurious effect of antibody (unpublished data). on the tumor and demonstrate that interaction between anti- Evidence that the interference with tumor rejection was body and one of the I-A gene products expressed in an F1 hy- mediated by antibodies with specificity for MHC-encoded brid is sufficient for the manifestation of antiserum activity. determinants rather than any contaminating antibody species Finally, it was possible to show that hyperimmune mice was provided by results of serum absorption experiments using pretreated with anti-K,I-A antiserum in vivo could no longer congenic cell populations. A more precise analysis of the anti- adoptively transfer effective S1509a tumor immunity to naive body specificities involved revealed that modulation of rejection recipients. Because the ability to transfer immune protection was mediated exclusively by antibodies directed against de- against tumor growth is dependent upon intact T-cell function terminants encoded by the I-A subregion of the H-2 complex, (5, 6, 25), it may be argued that this effect of the antiserum with no contribution by antibodies reacting with Kk determi- results from its interference with the generation and manifes- nants. Thus, it can be stated with a reasonable degree of assur- tation of effector T-cell activity. This may be due to a direct ance that the anti-I-Ak specificities present in this antiserum action of antibody on already primed effector cells, as suggested are the critical components responsible for interrupting immune by the presence of I region determinants on certain effector tumor rejection in mvio. It should also be noted that the in vivo cells for syngeneic tumors (25), or alternatively, it may reflect Downloaded by guest on September 28, 2021 924 Immunology: Perry et al. Proc. Natl. Acad. Sci. USA 76 (1979) the interruption of some critical event in the development and 1. Prehn, R. T. & Main, J. M. (1957) J. Natl. Inst. 18, differentiation of effector type cells. For example, antibody 769-778. administration may induce an alteration in the antigen-pre- 2. Foley, E. J. (1953) Cancer Res. 13,835-837. senting capacity of macrophages, resulting in less-efficient 3. Forbes, J. T., Nakao, T. & Smith, R. T. (1975) J. Exp. Med. 141, stimulation of responsive T cells. This is particularly relevant 1181-1200. in light of the idea that T cells recognize antigen in the context 4. Cerottini, J. C. & Brunner, K. T. (1974) Adv. Immunol. 18, 67-132. of I-A region-encoded Ia determinants expressed on the ma- 5. Rouse, B. T., Rollinghoff, M. & Warner, N. L. (1973) Eur. J. crophage surface. Immunol. 3, 218-224. An alternate hypothesis relates to the serum's potential for 6. Rouse, B. T., Rollinghoff, M. & Warner, N. L. (1972) Nature interference with helper T-cell function, either directly or by (London) New Biol. 238, 116-117. interaction with T cell-derived helper factor(s) (21). It is con- 7. Rollinghoff, M. & Wagner, H. (1973) Eur. J. Immunol. 3, ceivable that Ia determinant-bearing helper factor(s) may be 471-476. rendered ineffectual or express only minimal activity as a 8. Plata, F., Gomard, E., Leclerc, J. C. & Levy, J. P. (1973) J. Im- consequence of binding to antibody with anti-I-A specificity. munol. 111, 667-671. Because it is possible that helper factor(s) produced by the F1 9. Russell, S. W., Gillespie, G. Y. & McIntosh, A. T. (1977) J. Im- host bear Ia determinants encoded by either parental haplotype, munol. 118, 1574-1579. but not by both simultaneously, antibody-induced interference 10. Shin, H. S., Hayden, M., Langley, S., Kaliss, N. & Smith, M. R. with the expression of factor activity may be strictly quantita- (1975) J. Immunol. 114, 1255-1263. tive in nature, as reflected by the lack of complete tumor escape 11. Herberman, R. B, Nunn, M. E., Holden, H. T., Stall, S. & Djeu, in most cases. Indeed, it is not unreasonable to predict that other J. Y. (1977) Int. J. Cancer 19,555-564. cellular responses that are dependent on I-A determinant-re- 12. Haller, O., Hansson, M., Kiessling, R. & Wigzell, H. (1977) Nature stricted events may be diminished as well. (London) 270, 609-611. Thus, it can be concluded that the in vivo administration of 13. Lamon, E. W., Skurzak, H. M., Andersson, B., Whitten, H. D. antisera with the potential to interact with I-A determinants & Klein, E. (1975) J. Immunol. 114, 1171-1176. expressed on cells or factors of the immune host inhibits their 14. Herberman, R. B., Bartram, S., Haskill, J. S., Nunn, M., Holden, H. T. & West, W. H. (1977) J. Immunol. 119,322-326. capacity to mount a secondary response to tumor antigen. This 15. Greene, M. I., Dorf, M. E., Pierres, M. & Benacerraf, B. (1977) was determined by a decreased ability of the immune tumor- Proc. Natl. Acad. Sci. USA 74,5118-5121. bearing animal to reject tumor as well as by the apparent de- 16. Takei, F., Levy, J. G. & Kilburn, D. C. (1977) J. Immunol. 118, pletion of immunocompetent cells capable of adoptively 412-417. transferring immunity to naive recipients. These studies also 17. Fujimoto, S., Greene, M. I. & Sehon, A. H. (1976) J. Immunol. complement previous work on the modulation of tumor im- 116,791-799. munity by the manipulation of critical regulatory cell types. 18. Fujimoto, S., Greene, M. I. & Sehon, A. H. (1976) J. Immunol. Thus, it was possible to augment host effector responses by 116,800-806. elimination of suppressor T-cell activity by in vivo therapy with 19. Perry, L. L., Benacerraf, B., McCluskey, R. T. & Greene, M. I. antisera directed against determinants encoded by the I-J (1978) Am. J. Pathol. 92,491-506. subregion of the H-2 complex (15). It is of interest that both 20. Perry, L. L., Benacerraf, B. & Greene, M. I. (1978) J. Immunol. types of effects (increased or decreased tumor rejection) were 12, 2144-2147. obtained by the administration in vivo of only microliter 21. Benacerraf, B. & Germain, R. N. (1978) Immunol. Rev. 38, amounts of the relevant anti-Ia antisera. Collectively, these 70-119. results provide highly suggestive evidence for the critical role 22. Greene, M. I., Fujimoto, S. & Sehon, A. H. (1977) J. Immunol. of I-J and I-A determinant-bearing cells or their products in the 119,757-764. 23. Dorf, M. E., Toth, E. K. & Balner, H. (1972) Tissue Antigens 2, host response to syngeneic tumor challenge and support the 461-472. contention that it may be possible to regulate tumor immunity 24. Greene, M. I., Perry, L., Dorf, M. E. & Benacerraf, B. (1978) J. in vivo through the use of genetically defined antisera. Immunol. 121, 1616. This work was supported by Grants CA-14723, AI-13419, and AI- 25. Fujimoto, S., Matsuzawa, T., Nakagawa, K. & Tada, T. (1978) 00152 from the National Institutes of Health and by Grant PCM 75- Cell. Immunol. 38,378-387. 22422 from the National Science Foundation. L.L.P. was suppofted 26. Haagensen, D. E., Jr., Roloson, G., Collins, J. J., Wells, S. A., Jr., by a National Research Service Award from the Institute of General Bolognesi, D. P. & Hansen, H. J. (1978) J. Natl. Cancer Inst. 60, Medical Sciences (CA-09141-03). 131-139. Downloaded by guest on September 28, 2021