German researchers have developed a new Covid vaccine that is effective among people with weaker immune systems like cancer patients, particularly those with B-cell deficiencies. B cells are the immune cells responsible for antibody-mediated responses, which is the main target of all currently approved Covid vaccines. But cancer patients remain immunocompromised as treatments such as chemotherapies and some immunotherapies destroy B cells. The results presented at the recent AACR Annual Meeting 2022, showed that the vaccine CoVac-1 induced T-cell immune responses in 93 per cent of patients with B-cell deficiencies, including many patients with leukaemia and lymphoma, Medical Xpress reported.”To our knowledge, CoVac-1 is currently the only peptide-based vaccine candidate specifically developed and evaluated for immunocompromised patients,” said Juliane Walz, Professor at the University Hospital Tubingen in Germany. The CoVac-1 vaccine enhances the response from T cells – another type of immune cell, and “previous evidence has shown that T cells can combat Covid-19 even in the absence of neutralising antibodies,” said Claudia Tandler, a graduate student at the University. “T-cell immune responses against SARS-CoV-2 are of particular importance for patients with B-cell deficiencies, who develop very limited antibody responses after infection or vaccination,” Tandler added. To develop CoVac-1, Tandler and team chose six specific antigens from different parts of the virus (not limited to spike protein as the current vaccines) to make up their vaccine. CoVac-1 is a peptide vaccine, meaning that the protein pieces are injected directly, rather than being encoded via mRNA. “CoVac-1-induced T-cell immunity is far more intense and broader, as it is directed to different viral components than mRNA-based or adenoviral vector-based vaccines that are limited to the spike protein and are thus prone to loss of activity due to viral mutations,” Tandler said. In the phase I clinical trial, the researchers recruited 14 patients with a B-cell deficiency, including 12 patients with leukemia or lymphoma. The patients were given a single dose of CoVac-1 and monitored for up to six months for safety and immunogenicity. Notably, 64 per cent of the patients in this study had been previously vaccinated with an approved SARS-CoV-2 vaccine that failed to elicit a humoral immune response. Fourteen days after vaccination, T-cell immune responses were observed in 71 per cent of patients, which rose to 93 per cent of patients, 28 days after vaccination.