ALX148 is a High Affinity SIRPα Fusion that Blocks CD47, Enhances the Activity of Anti-Cancer Antibodies and Checkpoint Inhibitors, and Has a Favorable Safety Profile in Preclinical Models

Steven E Kauder, Tracy C Kuo, Amy Chen, Ons Harrabi, Sony S Rocha, Laura Doyle, Sangeetha Bollini, Bora Han, Emma Sangalang, Janet Sim, Sophia Randolph, Jaume Pons, and Hong I Wan

Alexo Therapeutics South San Francisco, CA USA Dublin, Ireland The CD47-SIRPα Interaction Regulates Myeloid Cell Function

• CD47 – Broadly expressed cell Myeloid Cell surface protein – Overexpressed on tumor cells Tumor Cell SIRPα CD47 Inflammation • SIRPα Activation – Receptor for CD47 on myeloid cells – Inhibitory signaling upon CD47 binding • CD47-SIRPα is an immune checkpoint • CD47 is a promising therapeutic target Unique Design of ALX148 is Responsible for Improved Safety ALX148 • Engineered SIRPα domain binds CD47 High Affinity with picomolar affinity SIRPα Domain S-S S-S • Blocks CD47-SIRPα interaction • Binds CD47 from humans, non-human primates, and mice Inactive Fc Domain • Fc domain does not bind Fcγ receptor, binding to neonatal Fc receptor is maintained Red Blood Cells Platelets ALX148 Control, active Fc ALX148 Control, active Fc 125 *** 150 **** 125 100 **** 100 75 75 50 50

25 25 % of Predose (Day -5) % of Predose (Day -5) 0 0 CD-1 mice -5 3 5 12 -5 3 5 12 -5 3 5 12 -5 3 5 12 30 mg/kg x1 Day Day ****p<0.0001, ***p<0.001 ALX148 Enhances Activity of Targeted Antitumor Antibodies

Phagocytosis of Daudi Inhibition of Z138 Xenograft Tumor Cells in vitro Tumorigenesis 2000 15 SEM +

1500 3 10 **** 1000

5 500 Phagocytosis, percent Tumor Volume, mm Volume, Tumor 0 0 -2 -1 0 1 2 3 14 16 18 20 22 24 26 28 30 32 34

ALX protein, nM (log10) Day post implant No antibody PBS obinutuzumab obinutuzumab ALX148 ALX148 ALX148 + obinutuzumab ALX148 + obinutuzumab Similar results with rituximab, trastuzumab

NOD SCID Mice 0.05 mg/kg obinutuzumab 2x/week 10 mg/kg ALX148 2x/week ****, p<0.0001 ALX148 Enhances Efficacy of Checkpoint Inhibitors in Multiple Syngeneic Models

Combination With Combination With αPD-1 in CT26 Model αPD- in MC38 Model 800 SEM ±

3 600

400 **** ** 200

Tumor volume, mm volume, Tumor 0 5 10 15 20 Days post implantation PBS anti-PD-L1 ALX148 ALX148 + anti-PD-L1

BALB/c mice C57BL/6 mice αPD-1 5 mg/kg 3q5d αPD-L1 2 mg/kg 2q7d ALX148 10 mg/kg 2q10d ALX148 30 mg/kg 2q10d **p<0.01 ****p<0.0001 ALX148 Activates Splenic Dendritic Cells in Tumor-Bearing Mice

CD8+ Dendritic Cells CD86 Expression SpleenCCR7 CCR7 Expression CD8+ DC of CD45 0.5 500 650 + ** ** * ** ** * ** * 0.4 600 450 550 0.3 400 500 0.2 450 350 0.1 400 Geometric Mean (MFI) Geo Mean(MFI) Geo Geo Mean(MFI) Geo PercentCD45 of 0.0 300 350 PBS ALX148 αPD-L1 ALX148 PBS ALX148 αPD-L1 ALX148 PBS ALX148 αPD-L1 ALX148 + + PBS + αPD-L1 αPD-L1 αPD-L1 30 ALX148 2 anti-PD-L1

30 ALX148/anti-PD-L1

C57BL/6 mice αPD-L1 2 mg/kg 2q7d ALX148 30 mg/kg 2q10d **p<0.01, *p<0.05 ALX148 and Anti-PD-L1 Cooperatively Increase CD8+ Function in the Tumor

Infiltrating CD8+ T Cells IFNγ+ CD8+ T Cells Granzyme B+ CD8+ T Cells **** ** **** **** * + + 0.8 + **** **** **** 0.6

0.4

0.2 PercentCD45 of PercentCD45 of 0.0 PercentCD45 of PBS ALX148 αPD-L1 ALX148 PBS ALX148 αPD-L1 ALX148 PBS ALX148 αPD-L1 ALX148 + + + αPD-L1 αPD-L1 αPD-L1

C57BL/6 mice αPD-L1 2 mg/kg 2q7d ALX148 30 mg/kg 2q10d ****p<0.0001, **p<0.01, *p<0.05 ALX148 Reduces Immunosuppressive Populations in the

Tumor-Associated Myeloid-Derived Suppressor Cells * ** 15 * ** * + *

10

5 M1/M2 Ratio M1/M2ratio PercentCD45 of 0 PBS ALX148 αPD-L1 ALX148 PBS ALX148 αPD-L1 ALX148 + + αPD-1 αPD-L1 BALB/c mice C57BL/6 mice CT26 tumor MC38 tumor αPD-1 5 mg/kg x1 αPD-L1 2 mg/kg 2q7d ALX148 30 mg/kg x1 ALX148 30 mg/kg 2q10d *p<0.05, **p<0.01 *p<0.05, **p<0.01 ALX148 Has a Favorable Safety Profile in Nonhuman Primates

• Four week repeat dose toxicity study • No ALX148 mechanism-related toxicity or adverse events up to 100 mg/kg • Separate PK/PD study: PK profile similar to CD47 antibody; Sustained CD47 target occupancy 12, 10 ALX148 Pharmacokinetics CD47 Occupancy on CD4+ T Cells 13, 10 ALX148 10000 125 14, 30 ALX148 Concentration - Time Profile 15, 30 ALX148 1000 100 g/ml

μ 100 75

10 50 ALX148 (ug/ml)

ALX148, 1 25 CD47 (%) Occupancy

0.1 % CD47 Occupancy, 0

D2 D3 D5 D7 D9 D2D3 D5 D7D8 D-2 D12 D14 D18 D22 D-2 D12 D14 D18 D22 D1 4hr D1 4hr Day Day Group 1: Rituximab Days Group 1: Rituximab Group 2: Rituximab + ALX148 10mg/kg 10Group mg/kg 2: Rituximab + ALX148 10mg/kg30Group mg/kg 3: Rituximab + ALX148 30mg/kg Group 3: Rituximab + ALX148 30mg/kgGroup 4: Rituximab + ALX273 30mg/kg Group 4: Rituximab + ALX273 30mg/kgGroup 5: Rituximab + ALX274 30mg/kg Group 5: Rituximab + ALX274 30mg/kg

! ! Summary

ALX148 Inhibits the CD47-SIRPα Checkpoint

ALX148 activates DCs, enhancing T cell priming ALX148 decreases suppressive cells

ALX148 enhances ALX148 increases phagocytosis cytotoxic T cell function

After Chen and Mellman, 2013 • ALX148 enhances the efficacy of antitumor and checkpoint inhibitor antibodies • ALX148 has a favorable preclinical toxicity profile Summary

ALX148 Inhibits the CD47-SIRPα Checkpoint

ALX148 activates DCs, enhancing T cell priming ALX148 decreases suppressive cells

ALX148 enhances macrophage ALX148 increases phagocytosis cytotoxic T cell function

After Chen and Mellman, 2013 • ALX148 is currently being investigated in a Phase 1 clinical trial (NCT03013218) – Clinical safety profile consistent with preclinical studies – Clinical data presented at 2017 SITC Annual Meeting