Stimulation of Potent Humoral and Cellular Immunity via Synthetic Dual-Antigen MVA-Based COVID-19 Vaccine COH04S1 in Cancer Patients Post Hematopoietic Cell Transplantation and Cellular Therapy

Abstract

Hematopoietic cell transplantation (HCT) and chimeric antigen receptor (CAR)-T cell patients are immunocompromised, remain at high risk following SARS-CoV-2 infection, and are less likely than immunocompetent individuals to respond to vaccination. As part of the safety lead-in portion of a phase 2 clinical trial in patients post HCT/CAR-T for hematological malignancies (HM), we tested the immunogenicity of the synthetic modified vaccinia Ankara-based COVID-19 vaccine COH04S1 co-expressing spike (S) and nucleocapsid (N) antigens. Thirteen patients were vaccinated 3-12 months post HCT/CAR-T with two to four doses of COH04S1. SARS-CoV-2 antigen-specific humoral and cellular immune responses, including neutralizing antibodies to ancestral virus and variants of concern (VOC), were measured up to six months post vaccination and compared to immune responses in historical cohorts of naïve healthy volunteers (HV) vaccinated with COH04S1 and naïve healthcare workers (HCW) vaccinated with the FDA-approved mRNA vaccine Comirnaty^® (Pfizer, New York, NY, USA). After one or two COH04S1 vaccine doses, HCT/CAR-T recipients showed a significant increase in S- and N-specific binding antibody titers and neutralizing antibodies with potent activity against SARS-CoV-2 ancestral virus and VOC, including the highly immune evasive Omicron XBB.1.5 variant. Furthermore, vaccination with COH04S1 resulted in a significant increase in S- and N-specific T cells, predominantly CD4⁺ T lymphocytes. Elevated S- and N-specific immune responses continued to persist at six months post vaccination. Furthermore, both humoral and cellular immune responses in COH04S1-vaccinated HCT/CAR-T patients were superior or comparable to those measured in COH04S1-vaccinated HV or Comirnaty^®-vaccinated HCW. These results demonstrate robust stimulation of SARS-CoV-2 S- and N-specific immune responses including cross-reactive neutralizing antibodies by COH04S1 in HM patients post HCT/CAR-T, supporting further testing of COH04S1 in immunocompromised populations.

Keywords: COVID-19; SARS-CoV-2; cellular response; hematopoietic cell transplantation (HCT); humoral response; immunosuppression; modified vaccinia Ankara (MVA); nucleocapsid; phase 2 clinical trial; spike; vaccination.

Figure 1

COH04S1-elicited humoral and T cell immunity in cancer patients post hematopoietic cell transplantation and cellular therapy. Patients (n = 13) were vaccinated two to four times with COH04S1, and blood samples were evaluated for SARS-CoV-2-specific humoral and T cell immunity at the indicated timepoints. (A) Binding antibodies. Binding antibody titers to spike (S, circles), receptor-binding domain (RBD, squares), and nucleocapsid (N, triangles) antigens were measured with quantitative ELISA. (B) NAb responses. 50% neutralizing antibody titers (NT50) against ancestral SARS-CoV-2 (Wuhan-Hu-1, circles), Beta (squares), Delta (up-pointing triangles), and Omicron BA.1 (down-pointing triangles) and XBB.1.5 (diamonds) variants were measured using a pseudovirus (PsV) assay. Dotted lines represent the lower limit of detection. (C) IFNγ T cells. IFNγ T cells were quantified via ELISPOT following stimulation of PBMCs with S (circles), N (squares), and membrane (M, triangles) peptide libraries. Shown are the IFNγ spot forming units (SFU) measured in 10⁶ PBMCs. Dotted line represents the arbitrary threshold for a positive response (50 SFU/10⁶ PBMCs). (D) Activation-Induced Markers (AIM⁺) T cells. CD4⁺ and CD8⁺ AIM⁺ T cells per μL of blood were quantified via cytofluorimetry in PBMCs stimulated with S (CD4⁺ and CD8⁺ AIM⁺ T cells indicated as circles and up-pointing triangles, respectively) and N (CD4⁺ and CD8⁺ AIM⁺ T cells indicated as squares and down-pointing triangles, respectively) peptide libraries. Data are presented as box plots extending from 25th to 75th percentile, with lines indicating medians, and whiskers going from minimum to maximum values. Student’s t test on log10-transformed data was applied to compare baseline to post-vaccine geometric mean fold rise (GMFR) values. p values ≤ 0.05 are indicated. Where not indicated, p > 0.05.

Figure 2

Immunogenicity of COH04S1 in HCT/CAR-T patients and COH04S1 or Comirnaty^® in healthy adults. SARS-CoV-2 binding antibodies (IgG) to SARS-CoV-2 spike (S, (A)), nucleocapsid (N, (B)), neutralizing antibody titers to SARS-CoV-2 Wuhan-Hu-1 ancestral strain (C), and XBB.1.5 variant (D), and IFNγ T cells specific for SARS-CoV-2 S (E) and N (F) were measured in samples of COH04S1-vaccinated HCT/CAR-T patients (circles) at baseline (n = 13), day 56 (n = 12), and 180 (n = 6) post vaccination, and compared to responses measured in healthy volunteers (HV, squares, d0-d56 n = 9, d180 n = 6) vaccinated with COH04S1 or healthcare workers (HCW, triangles, n = 17) vaccinated with the FDA-approved mRNA vaccine Comirnaty^® at the same timepoints. Dotted lines in (C,D) represent the lower limit of detection. Dotted lines in (E,F) represent the arbitrary threshold of positivity (50 spots/10⁶ cells). At the day 180 timepoint, 4/6 HCT/CAR-T patients had received three/four COH04S1 doses. Data are presented as box plots extending from 25th to 75th percentile, with lines indicating medians, and whiskers going from minimum to maximum values. Values were compared using the two-tailed Mann–Whitney test. p values ≤ 0.05 are indicated. Where not indicated, p > 0.05.