Project 3: Checkpoint Receptor Targeting to Enhance Cetuximab Efficacy against HNSCC

Robert L. Ferris, MD, PhD, FACS, Co-Leader
Dario A.A. Vignali, PhD, Co-Leader

Despite overexpression of the epidermal growth factor receptor (EGFR) on nearly all head and neck squamous cell carcinomas (HNSCC), the EGFR-specific monoclonal antibody (mAb) cetuximab is effective only in a minority of patients. The modest effects of cetuximab have stimulated interest in determining its anti-tumor mechanisms and the factors that limit clinical responses, in order to improve its efficacy by combining immunotherapeutic approaches. A growing body of evidence, and our preliminary results, indicate that a tumor antigen (TA)-specific mAb, such as cetuximab, can effectively trigger TA-specific cytotoxic T lymphocyte (CTL) responses. However, these effector CTLs are not fully effective, raising the possibility that inhibitory mechanisms limit the efficacy of cetuximab in the majority of patients. Blockade of these inhibitory mechanisms could restore anti-tumor activity and enhance cetuximab efficacy. However, the inhibitory mechanism(s) that are primarily responsible for limiting cetuximab efficacy remain unknown.

A high frequency of peripheral blood T-lymphocytes (PBL) and tumor infiltrating T-lymphocytes (TIL) in multiple solid tumors, including HNSCC, express elevated levels of inhibitory receptors (so-called “checkpoints”), such as cytotoxic T lymphocyte antigen (CTLA-4) and programmed death-1 (PD-1), rendering them unresponsive to antigenic stimulation (exhaustion). Furthermore, CTLA-4+ regulatory T cells (Tregs), a potently suppressive sup-population of CD4+ T cells that produce tumor growth factor beta (TGF-β), are often present at increased frequencies and with enhanced suppressive capacity in tumors. Collectively, inhibitory receptors on CTL and Tregs are major barriers to effective anti-tumor T cell responses, which has been demonstrated by striking clinical responses to anti-CTLA-4 and anti-PD-1 antibodies. Our previous studies and preliminary data support a working model in which the generation of TA-specific CD8+ T cells triggered by cetuximab in the non-responder patient population occurs concurrently with increased inhibitory mechanisms (including TGF-β) that reduce the clinical response to cetuximab therapy. This project will take advantage of the availability of biospecimens from two novel Hillman clinical trials, which have either recently completed (Hillman 08-013, testing immune biomarkers in single-agent cetuximab treated patients) or are ongoing (Hillman 12-084, combining cetuximab with anti-CTLA-4 mAb ipilimumab to inhibit Treg). We will determine whether inhibitory mechanisms are responsible for limiting anti-tumor activity induced in cetuximab-treated HNSCC patients and directly assess the impact of CTLA4+ Tregs in this new, ongoing clinical trial.

Aim 1: Determine the extent to which inhibitory mechanisms are altered in tumors from HNSCC patients, and whether this correlates with CTL activity and clinical responsiveness. We will determine the effect on EGFR blockade by cetuximab on the expression of checkpoint inhibitory receptors and ligands, and the on the number, function and stability of Tregs. Using banked, paired PBL/TIL and tumor samples from 40 HNSCC patients treated on a single agent, neoadjuvant cetuximab trial (Hillman 08-013), we will: 1) evaluate the upregulation of inhibitory receptors on CTL and Treg; 2) assess the state of CTL exhaustion and determine the stability and function of Tregs; 3) determine inhibitory ligand expression on HNSCC and intratumoral antigen presenting cells (APCs); 4) assess whether PD-L1 expression in HNSCC tumor tissues is JAK/STAT dependent; and 5) determine whether cetuximab therapy modulates the functional activity of myeloid intratumoral APCs. We will attempt to correlate these findings with clinical response to cetuximab therapy.

Aim 2: Determine the frequency and phenotype of CTL and Tregs in a phase Ib trial of concurrent cetuximab/radiotherapy plus ipilimumab (anti-CTLA-4) in locally advanced HNSCC. We will take advantage of a novel combinatorial immunotherapy trial of cetuximab/radiation plus ipilimumab (Hillman 12-084); one of the first to our knowledge that combines an anti-tumor mAb with an anti-inhibitory receptor mAb. Using TIL/PBL and tumor samples, we will: 1) translate our findings in the Hillman 12-084 trial in HPV+ and HPV- advanced HNSCC; and determine if clinical responses are predicted by: 2) inhibitory receptor expression on circulating and intratumoral T cells; 3) inhibitory receptor expression on TA-specific T cells; 4) compensatory upregulation of alternative inhibitory receptors (e.g., PD-1); and/or 5) expression of inhibitory ligands in the tumor microenvironment. These results and potential biomarkers may inform future combination therapies.