G1 Therapeutics, Inc. announced results from an immunologic analysis of Phase 2 study data showing that trilaciclib enhances both CD4 and CD8 T cell function in certain patients with metastatic triple negative breast cancer (mTNBC) when administered prior to chemotherapy. Patients receiving placebo prior to chemotherapy did not demonstrate enhanced T cell function. In the exploratory analysis, researchers sought to investigate the immune mechanisms underlying the improved rate of overall survival shown in the 2020 Phase 2 trial of TNBC patients receiving trilaciclib in combination with gemcitabine/carboplatin (GCb) compared with GCb alone. The researchers evaluated tumor samples and peripheral blood samples from patients at baseline and after trilaciclib/GCb administration or after placebo/GCb administration to identify differential gene expression and changes in immune function between the two groups. Further, they measured qualitative and quantitative differences between patients who did respond or did not respond to trilaciclib plus GCb. Response to treatment was defined as partial or complete response, while nonresponse was defined as stable or progressive disease.