according to study results presented at the annual meeting of the American Association for Cancer Research.
The phase 1/2 trial included 54 patients with a B-cell deficiency (mean age, 63 years; 28% female): 4 had congenital B-cell deficiency and 50 had a blood cancer (lymphocytic leukemia or lymphoma). T-cell immune responses were observed in 86% of patients 28 days after vaccination with a single CoVac-1 dose. The potency of CoVac-1–induced T-cell responses exceeded those seen typically with B cell–deficient patient responses after mRNA vaccine treatment and were comparable with those seen among nonimmunocompromised COVID-19 patients.
In the majority of individuals, currently approved SARS-CoV-2 vaccines induce a robust immune response, however, their efficacy, has been shown to be decreased among individuals who are immunocompromised. Patients treated for hematologic cancers, in particular, receive treatment regimens that damage healthy immune cells, particularly B cells, said Juliane Walz, MD, the study’s senior author and professor of medicine at University Hospital Tübingen (Germany).
“In the clinic, we see many cancer patients who do not mount sufficient humoral immune responses after vaccination with available SARS-CoV-2 vaccines,” Dr. Walz said. “These patients are at a high risk for a severe course of COVID-19.”
B-cell deficiency, she stated, can be compensated for by enhancing T-cell responses against SARS-CoV-2, which can then combat infections in the absence of neutralizing antibodies.
In a prior study of CoVac-1 among 36 adults without immune deficiency, the vaccine elicited T-cell responses that were still robust 3 months post vaccination, and that included responses against omicron and other key SARS-CoV-2 variants.
While mRNA-based or adenoviral vector-based vaccines are limited to the spike protein and are thus prone to loss of activity because of viral mutations, CoVac-1–induced T-cell immunity is far more intense and broader, Dr. Walz said.
CoVac-1 is a peptide vaccine that is injected directly rather than being encoded via mRNA and targets different viral components. It would not be given, however, to healthy, immunocompetent adults because it is important for them to have both B-cell antibody and T-cell response.
The patients with B-cell deficiency recruited for the study were given a single dose of CoVac-1 and assessed for safety and immunogenicity until day 56. Prior vaccinations with an approved SARS-CoV-2 vaccine had failed to elicit a humoral response in 87% of the subjects.
“Our vaccine does not induce antibody responses,” Dr. Walz said. “However, it could be used to induce broad T-cell responses as a complementary or additive vaccine for elderly adults. In the elderly, antibody responses decline very, very fast after vaccination.”
Dr. Walz said that CoVac-1 could find application in various syndromes associated with congenital B-cell deficiencies, in autoimmune diseases such as rheumatoid arthritis and multiple sclerosis, or diseases treated with rituximab or other B cell–depleting therapies (for example, ofatumumab, blinatumomab, or chimeric antigen receptor T cells), and in transplant patients.
A phase 3 study of CoVac-1 versus placebo is under discussion and would require about 300-500 subjects, Dr. Walz said.
“CoVac-1 is designed to induce broad and long-lasting SARS-CoV-2 T-cell immunity, even in individuals who have impaired ability to mount sufficient immunity from a currently approved vaccine, and thus protect these high-risk patients from a severe course of COVID-19,” Dr. Walz said.
“Having an option for these patients is just critical – so this is significant work,” said Ana Maria Lopez, MD, MPH, of the Sidney Kimmel Cancer Center–Jefferson Health, Philadelphia.
Limitations of this study included the small sample size with low racial and ethnic diversity, Dr. Walz stated.
Funding was provided by the Ministry of Science, Research and the Arts of the state of Baden-Württemberg; the Federal Ministry of Research and Education in Germany; the German Research Foundation under Germany’s Excellence Strategy; and the Clinical Cooperation Unit Translational Immunology at University Hospital Tübingen. Dr. Walz holds the CoVac-1 patent.