# Evaluation of HVEM and PD-L1 Expression Profile in Tumors as Potential Predictive Biomarkers for HFB200603, a BTLA Antagonist, as Monotherapy and in Combination with Tislelizumab

### Authors
María de Miguel, Eladio Marquez, Germain Margall-Ducos, Victor Moreno, Valentina Gambardella, Gennaro Daniele, Jessica Menis, Ana Landa Magdalena, Anthony B. El-Khoueiry, Emiliano Calvo, Alice Rossi, Francesca Zacchi, Olja Rapaic, Melissa Harney, Juying Li, Hombline Poullain, Alexander Chung, Francisco Adrian, Jinping Gan

### Institutions
START Madrid-CIOCC, Centro Integral Oncológico Clara Campal, HiFiBiO Therapeutics Inc., START Madrid - Hospital Fundación Jiménez Díaz, Hospital Clinico Universitario de Valencia, Fondazione Policlinico Universitario Agostino Gemelli IRCCS – Università Cattolica del Sacro Cuore, Azienda Ospedaliera Universitaria Integrata di Verona, Clinica Universidad de Navarra, University of Southern California Norris Comprehensive Cancer Center.

### Background
- BTLA is a co-inhibitory immune checkpoint molecule primarily expressed on B cells, T cells, and dendritic cells. The binding of HVEM to BTLA induces the recruitment of SHP1 and SHP2, leading to the inhibition of T cell proliferation and cytokine production.
- Previously, we reported Phase 1 results that demonstrated a tolerable safety profile and clinically meaningful efficacy with HFB200603 as monotherapy and in combination with tislelizumab (TIS) in advanced refractory solid tumors.
- In addition, we report potential biomarkers predictive of response to HFB200603 monotherapy and in combination with TIS.

### Study Design and Patient Demographics
*DL (Dose Level); HFB (HFB200603); Q3W (once every 3 weeks); TIS (tislelizumab)*

### Demographics and Clinical Characteristics 
| Characteristic | Monotherapy (n=17) | Combination (n=43) |
| --- | --- | --- |
| Median age, years (range) | 62 (39-77) | 63 (44-82) |
| Female | 6 (35) | 15 (35) |
| Male | 11 (65) | 28 (65) |
| ECOG PS 0 | 13 (76) | 27 (63) |
| ECOG PS 1 | 4 (24) | 16 (37) |
| Median time since initial diagnosis (range), years | 2.5 (0.9-13.7) | 3.5 (0.4-24.3) |
| Median number of prior systemic cancer therapy regimens (range) | 3 (1-4) | 3 (1-7) |
| Received prior anti-PD-(L)1 therapy: Yes | 8 (47) | 22 (51) |
| Received prior anti-PD-(L)1 therapy: No | 9 (53) | 21 (49) |
| Median follow-up time (range), months | 2.7 (0.9-12.0) | 3.5 (0.5-18.2) |
| Tumor types, PD-L1+ Colorectal cancer | 7 (41) | 14 (33) |
| Tumor types, Clear cell renal cell carcinoma | 3 (18) | 9 (21) |
| Tumor types, PD-L1+ Non-small cell lung cancer | 3 (18) | 8 (19) |
| Tumor types, PD-L1+ Gastric cancer | 3 (18) | 7 (16) |
| Tumor types, PD-L1+ Melanoma | 1 (6) | 5 (11) |

ECOG PS, Eastern Cooperative Oncology Group performance status; PD-(L)1, programmed cell death protein (ligand) 1.

- Grade 3 TRAEs in 3 of 5 subjects were lab abnormalities (AST/ALT, lipase increase) which quickly resolved without medication.
- HFB200603 monotherapy was well tolerated with treatment-related adverse events (TRAEs) limited to Grade 1 and no Grade 3.
- HFB200603 + TIS was also well tolerated with TRAEs mostly Grade 1-2 and few incidences of Grade 3.

### Safety Profile
| Adverse Event | Treatment Related Adverse Events (TRAE), ≥2 Incidence or Grade 3 |
| --- | --- |
| HFB200603 Monotherapy (n=17) |  |
| Any, n (%) | Gr 1, n (%) | Gr 2, n (%) | Gr 3, n (%) 
| Overall | 6 (35) | 6 (35) | 1 (6) |
| ALT / AST increased | 1 (6) | 1 (6) | - |
| Anemia | - | - | - |
| Amylase increased | - | - | - |
| Arthralgia | - | - | - |
| Diarrhea | 1 (6) | 1 (6) | - |
| Fatigue / Asthenia | 5 (29) | 5 (29) | - |
| Lipase increased | - | - | - |
| Myalgia | 1 (6) | 1 (6) | - |
| Nausea | 1 (6) | 1 (6) | - |
| Pneumonitis | - | - | - |
| Pruritus | 1 (6) | 1 (6) | - |
| Rash / dermatitis acneiform / psoriasis | - | - | - |
| Thrombocytopenia | - | - | - |

### Potential Baseline Biomarkers Predictive of Response to HFB200603 ± TIS
- HFB200603 monotherapy efficacy observed with preliminary clinical activities.
- Tumor – mIF: HVEM and PD-L1 expression on immune cells may be predictive of responses.
- Increased levels of HVEM expressing CD8 T cells may be predictive of prolonged PFS in response to HFB200603 monotherapy.
- Higher expression levels of HVEM and PD-L1 on immune-suppressing macrophages may be predictive of prolonged PFS in response to HFB200603 + TIS combination.

### Summary
- Integrative analysis of tumor mIF dataset identified biomarkers potentially predictive of responses.
- HVEM+CD8T aligns with HFB200603 MOA in activating BTLA+ CD8 T cells.
- CPS may be a surrogate for selecting patients with higher HVEM+ PDL1+ macrophages as a potential response enrichment strategy. 
- MSS-CRC and ccRCC warrant further evaluation with additional patients.

We extend our thanks to the patients, their families, and the investigators and staff members who made this trial possible.

1. de Miguel. et al., (2024) ESMO 2024. Barcelona, Spain.
Study sponsored by HiFiBiO Inc.