Extended evaluation of a phase 1/2 trial on dosing, safety, immunogenicity, and overall survival after immunizations with an advanced-generation Ad5 [E1-, E2b-]-CEA(6D) vaccine in late-stage colorectal cancer

Abstract

A phase 1/2 clinical trial evaluating dosing, safety, immunogenicity, and overall survival on metastatic colorectal cancer (mCRC) patients after immunotherapy with an advanced-generation Ad5 [E1-, E2b-]-CEA(6D) vaccine was performed. We report our extended observations on long-term overall survival and further immune analyses on a subset of treated patients including assessment of cytolytic T cell responses, T regulatory (Treg) to T effector (Teff) cell ratios, flow cytometry on peripheral blood mononuclear cells (PBMCs), and determination of HLA-A2 status. An overall survival of 20 % (median survival 11 months) was observed during long-term follow-up, and no long-term adverse effects were reported. Cytolytic T cell responses increased after immunizations, and cell-mediated immune (CMI) responses were induced whether or not patients were HLA-A2 positive or Ad5 immune. PBMC samples from a small subset of patients were available for follow-up immune analyses. It was observed that the levels of carcinoembryonic antigen (CEA)-specific CMI activity decreased from their peak values during follow-up in five patients analyzed. Preliminary results revealed that activated CD4+ and CD8+ T cells were detected in a post-immunization sample exhibiting high CMI activity. Treg to Teff cell ratios were assessed, and samples from three of five patients exhibited a decrease in Treg to Teff cell ratio during the treatment protocol. Based upon the favorable safety and immunogenicity data obtained, we plan to perform an extensive immunologic and survival analysis on mCRC patients to be enrolled in a randomized/controlled clinical trial that investigates Ad5 [E1-, E2b-]-CEA(6D) as a single agent with booster immunizations.

Fig. 1

Kaplan–Meier survival plots on long-term overall survival of treated mCRC patients. a Represents all treated patients. b Represents patients that received all three treatments. c Represents patients immunized three times with the two highest doses of vaccine. There were 23 events during the study

Fig. 2

Profiles of CEA-directed CMI responses in five mCRC patients during and after the course of immunotherapy. Note the decrease in CMI responses from their peak values after immunizations ended. Values are mean ± SEM

Fig. 3

CTL responses (ELISpot granzyme B secretion) were assessed pre-treatment (week 0) and post-treatment (week 6–9). Note the increase in CTL activity after immunizations of mCRC patients (P < 0.05 Wilcoxon test). Values are mean ± SEM

Fig. 4

Treg/Teff ratios in five mCRC patients during and after immunotherapy. Ratios increased in one patient (031) and increased with a return to baseline ratio in another patient (501). Ratios decreased with a return to baseline ratio at 52 weeks in one patient (005). Ratios were decreased in two of the other five patients (024 and 507)

Fig. 5

Ad5 NAb titers over time in six mCRC patients immunized with Ad5 [E1-, E2b-]-CEA(6D). Titers increased in all patients by week 9 (3 weeks after the last immunization) and then decreased thereafter