GeoVax's COVID-19 Vaccine Shows Superior T-Cell Response in CLL Patients, Prompts Trial Design Change
Key Insights
GeoVax's GEO-CM04S1 COVID-19 (search) vaccine demonstrated superior T-cell responses compared to Pfizer-BioNTech (search)'s vaccine in chronic lymphocytic leukemia (search) patients, with 40% meeting the primary endpoint versus 14.3% for the mRNA vaccine.
The trial's Data and Safety Monitoring Board discontinued the comparator arm after the mRNA vaccine failed to meet the predefined primary immunogenicity endpoint, allowing the study to proceed exclusively with GEO-CM04S1.
The dual-antigen MVA-vectored vaccine generated approximately 10-fold higher nucleocapsid-specific CD4 T-cell (search) activation and maintained responses through Day 180, addressing critical gaps for immunocompromised populations.
GeoVax Labs (search) announced that its next-generation COVID-19 (search) vaccine GEO-CM04S1 demonstrated superior T-cell responses compared to Pfizer-BioNTech (search)'s BNT162b2 vaccine in patients with chronic lymphocytic leukemia (search) (CLL), according to interim Phase 2 data published in the British Journal of Haematology. The findings led the trial's Data and Safety Monitoring Board to discontinue the comparator arm and proceed exclusively with the experimental vaccine.
Superior Immunogenicity in Difficult-to-Vaccinate Population
The Phase 2 study (NCT05672355) enrolled 31 CLL patients previously vaccinated with mRNA vaccines, with 27 evaluable for primary analysis. GEO-CM04S1 achieved the primary endpoint in 40% of recipients compared to 14.3% for BNT162b2, defined as a greater than or equal to 3-fold rise in antigen-specific IFN-γ (search)-secreting T cells at Day 56.
The dual-antigen vaccine demonstrated higher Spike-specific IFN-γ (search) responses at Days 28, 56, and 84, with approximately 10-fold higher nucleocapsid-specific CD4 T-cell (search) activation compared to BNT162b2. Importantly, these responses were maintained through Day 180, indicating durability of the immune response.
DSMB Decision Validates Clinical Approach
Following interim analysis, the trial's Data and Safety Monitoring Board ruled to discontinue the randomized, double-blind comparator arm after the mRNA vaccine failed to meet the predefined primary immunogenicity endpoint. This decision allows enrollment to proceed exclusively in a single-arm cohort receiving GEO-CM04S1.
"These results demonstrate GEO-CM04S1's ability to address the immune limitations of CLL patients by inducing strong, durable T-cell responses to both spike and nucleocapsid proteins of SARS-CoV-2 (search)," stated Kelly T. McKee, MD, MPH, Chief Medical Officer. "The DSMB's decision to discontinue the comparator arm further validates the vaccine's clinical relevance for immunocompromised individuals."
Addressing Unmet Medical Need
GEO-CM04S1's performance addresses a critical gap for immunocompromised patients who generally respond suboptimally to vaccines designed to induce humoral (antibody) responses. More than 40 million adults in the U.S. and 400 million globally have some degree of compromised immunity, many of whom fail to mount meaningful responses to currently authorized COVID-19 (search) vaccines.
The vaccine's dual-antigen (Spike + Nucleocapsid), MVA-based platform promotes robust, durable T-cell responses that are less impacted by immune dysfunction and viral variation. Despite CLL-associated humoral defects, GEO-CM04S1 generated sustained nucleocapsid-IgG and demonstrated correlation between nucleocapsid-specific antibodies and T-cell activation, while mRNA vaccination produced higher early RBD-IgG titers but limited cellular immunity.
Broader Clinical Development Program
GEO-CM04S1 is currently being evaluated in multiple Phase 2 trials, including primary vaccination for immunocompromised individuals and booster vaccination for CLL patients. The vaccine has generated robust immune responses in difficult-to-vaccinate populations including CAR-T and stem-cell transplant recipients, who typically fail to respond well to first-generation vaccines.
Commercial Potential
Chairman and CEO David Dodd emphasized the commercial significance: "With more than 40 million immunocompromised Americans, many of whom lack durable protection from first-generation vaccines, GEO-CM04S1 represents a purpose-built solution for high-risk patients. This peer-reviewed publication strengthens our regulatory and partnering strategy as we advance toward potential commercialization."
The company estimates these patient segments represent a $30 billion-plus annual potential commercial market. The multi-antigen design stimulates immune responses that appear to be more durable and variant-resilient than single-antigen mRNA approaches.
Safety Profile
The study reported no Grade 3 or higher adverse events, supporting the vaccine's safety profile in this vulnerable patient population. The trial assessed T-cell responses, binding and neutralizing antibodies, and safety parameters throughout the study period.