Background Checkpoint inhibitors (CPI) have null objective response (ORR) and dismal disease control rates (DCR) in microsatellite-stable colorectal (MSS-CRC) and pancreatic cancer (PaC), due to low mutation burden and sparse T-cell infiltration. Liver metastases are common in these indications and are harder to infiltrate, further reducing the efficacy of immunotherapy. NT-I7 (efineptakin alfa) in combination with pembrolizumab has been shown to increase T-cell infiltration. This study explores the ability of NT-I7 and pembrolizumab to support T-cell infiltration in subjects with liver metastasis as a correlate of clinical efficacy.

Methods Open-label, phase 2a study in subjects with relapsed/refractory (r/r) CPI-naïve MSS-CRC and PaC. Subjects received NT-I7 at 1200 µg/kg every 6 weeks (Q6W) plus pembrolizumab at 200 mg Q3W. Antitumor activity was assessed by RECIST v1.1 and iRECIST. Pre-treatment and on-treatment biopsies were analyzed by Lunit SCOPE IO, an artificial intelligence-powered H&E analyzer, and immunohistochemistry. For exome sequencing analysis, single nucleotide variants and indels were detected and filtered by GATK Mutect2.

Results As of April 29, 2022, 53 subjects were evaluable. 67.9% of subjects had ≥2 prior therapies; 73.6% had liver metastasis and median tumor mutation burden (TMB; n=18) was 3.22 mutations/megabase. ORR was 3.8% per RECIST and 9.4% per iRECIST. Total density of tumor-infiltrating lymphocytes (TIL) significantly increased on-treatment, despite low TMB. Subjects with metastasis to sites other than the liver had 28.6% iORR and 71.4% iDCR, a remarkable result considering the lack of response with anti-PD(L)1 monotherapy, and significantly higher overall survival (OS; p=0.0241). However, NT-I7 and pembrolizumab still demonstrated benefit for patients with liver metastasis; with an iDCR of 25.6%. CD8 T-cell infiltration increased with treatment regardless of tissue location, including liver biopsies (p=0.0032). Lymphoid aggregates containing CD8+TCF1+ lymphocytes, suggestive of tertiary lymphoid structures, were observed on-treatment (n=14) in both liver and non-liver biopsies, including all 3 patients with objective response. Moreover, CD8+ T-cell infiltration was directly associated with OS (p=0.0002), suggesting that NT-I7 plus pembrolizumab increases intratumoral TIL density and CD8 T-cell infiltration in primary and metastatic locations to mediate clinical benefit.

Conclusions NT-I7 plus pembrolizumab shows remarkable efficacy in immunologically cold CPI-naïve r/r MSS-CRC and PaC in the absence of liver metastasis. Furthermore, this combination also increases T-cell infiltration in immune-excluded liver biopsies, favoring a hot tumor microenvironment that contributes to the overall high iDCR observed in these hard-to-treat CPI-resistant indications.

Acknowledgements The authors thank ICON for their partnership in conducting this trial.

Trial Registration NCT04332653

Ethics Approval The trial was approved by MD Anderson IRB, Advarra IRB, Mary Crowley IRB, and Integ Review IRB.