Effect of CTLA-4 overexpression on response to ipilimumab in melanoma.

Abstract

190 Background: CD8 positive tumor infiltrating lymphocytes (TILS) are highly associated with immune response and prognosis, and are also under investigation as a marker of response to checkpoint inhibitors. Given lack of predictive biomarkers for ipilimumab, growing number of trials for new indications for combination ipilimumab + nivolumab, and evidence to support therapeutic target overexpression as markers of response, we examined the role of CTLA-4 expression and TILS in response to ipilimumab and combination ipilimumab + nivolumab in melanoma. Methods: Formalin-fixed paraffin embedded melanoma samples taken prior to treatment by ipilimumab (n = 36) or combination ipilimumab + nivolumab (n = 10) were evaluated by a comprehensive immune gene expression profile to establish the relationship between CTLA-4 and CD8 and therapeutic response (RECIST v1.1). Results: Increased CTLA-4 expression was moderately associated with increased TILS (r2= .41, p = .004). This was observed in the monotherapy group (r2= .38, p = .02), and was higher in the smaller combination therapy group, though not statistically significant (r2= .59, p = .06). Higher levels of TILS were observed in responders who achieved clinical benefit from either regimen within 6 months (n = 20). No significant difference was observed between responders (M = 57.1, SD = 30.2) and nonresponders (M = 48.6, SD = 32.9); t(44) = -.895, p = .376. Lower levels of CTLA-4 were observed in responders who achieved clinical benefit from either regimen within 6 months. No significant difference was observed between responders (M = 54, SD = 35) and nonresponders (M = 38.7, SD = 26.8); t(44) = 1.70, p = .09. The ratio of TILS to CTLA-4 expression was higher in responders who achieved clinical benefit within 6 months (n = 20).No significant difference was observed between responders (M = 5.2, SD = 14.0) and nonresponders (M = 1.4, SD = 2.7); t(41) = -1.2, p = .212. Conclusions: While not statistically significant, CTLA-4 expression in melanoma patients treated with either ipilimumab or combination ipilimumab + nivolumab was lower in responders compared to nonresponders. This analysis does not support the concept that over-expression of CTLA-4 is a biomarker of response to anti-CTLA-4 therapy.