Immune Cell Infiltration within Differing Renal Cell Carcinoma Primary Histologies: Preliminary Report

The amount of tumor-infiltrating cells in renal cell carcinoma (RCC) has been associated with response to immunotherapy and prognosis. In this exploratory study we aim to characterize immune cell penetration within the RCC tumor microenvironment based on primary histologies of clear cell RCC (ccRCC), papillary RCC (pRCC), chromophobe RCC (chRCC) and unclassified RCC (uRCC).

Tumor and normal kidney tissue from 56 patients who underwent surgical excision from 12/2015–7/2017 were prospectively collected for analysis. Forty-five patients had ccRCC, 2 pRCC, 5 chRCC, and 4 uRCC. Immune cell phenotyping was performed using staining single-cell suspensions followed by flow cytometry. The mean differences in immune cell populations within the matched tumor-normal samples were analyzed by primary histology. Cell types analyzed included CD45+ cells (general marker of immune cells), CD3+ T cells, CD4+ T cells, CD8+ T cells, and CD4CD25+ Tregs. P-values were calculated by comparing ccRCC to the other primary histologies using two-sample T-tests with a pre-specified rejection level of 0.05.

Median age of this cohort was 59 years, with 69.6% male and 21 (37.5%) presenting with metastatic disease. Median tumor pathological size was 8.6 cm (2.9–18.1), and 41 (73.2 %) had pT3-pT4 disease. An enrichment of CD45+ cells were identified in 82.14 (%) of tumors compared to their corresponding normal tissue. The mean difference in CD45+ cells between matched samples in ccRCC, chRCC, pRCC, and uRCC was 33.97 (p<0.001), 13.71 (p<0.001), 13.91 (p=0.27), and -0.73 (p=0.97), respectively, Figure 1. Interestingly, a mean difference of -0.73 (p=0.97) in uRCC suggests fewer immune cells were found within the tumor than normal kidney. When comparing the mean differences in CD45+ across all histologies, we found a significant difference between immune infiltration in ccRCC and chRCC of 20.3 (95%CI 9.8-30.6, p=0.0004), figure 1. The observed trend of elevated immune cell infiltration across histologies was not limited to a specific cell type as all types analyzed (CD45 (p<0.001), CD3 (p<0.001), CD4 (p<0.0029), CD8 (p<0.001), CD4CD25 (p<0.001)) experienced a universal increase.

Our exploratory study showed a higher proportion of immune cells (CD45+) in tumor tissue compared to normal kidney especially in ccRCC tumor samples. Interestingly among the 4 uRCC patients, fewer immune cells were found in the tumor relative to normal kidney perhaps suggestive of immune exclusion. Elucidating these immune cell infiltration signatures may correlate with clinical outcomes and help identify those likely to benefit from immunotherapy. Further refinement of immune profile differences and validation of these findings in a larger cohort is currently ongoing.