People with blood cancer usually have a weak immune system, putting them at an increased risk of becoming very ill from COVID-19.

Furthermore, several cancer treatments cause these individuals to develop little or no antibodies against SARS-CoV-2 after COVID-19 vaccination. On the other hand, vaccination can activate T cells, which are responsible for the long-term immune response.

A team led by physicians Dr. Andrea Keppler-Hafkemeyer and Dr. Christine Greil from the Medical Center-University of Freiburgand virologist Prof. Oliver T. Keppler from LMU Munich has now characterised in detail the course over several months of the immune response of patients with blood cancer who had received a total of three vaccinations against COVID-19.

The results allow inferences to be made about the protection that vaccination gives these patients against serious illnesses from SARS-CoV2. Strong T cell response to COVID-19 vaccination.

The study focused on patients with two kinds of blood cancer: B-cell lymphoma and multiple myeloma. "Our results show that almost all study participants had a strong T cell response to COVID-19 vaccination," explains Dr. Andrea Keppler-Hafkemeyer.

"This could be one reason why breakthrough infections turned out to be mild to moderately severe even in study participants who had been unable to form any specific antibodies after vaccination because of their therapy," adds Dr. Christine Greil.

The co-principal investigators and lead authors regularly look after blood cancer patients in the Department of Medicine I at the Medical Center -- University of Freiburg.

The research group led by Prof. Oliver T. Keppler is specialised not only in analysing the concentration of antibodies after vaccination but also their quality.

This depends particularly on the strength of the bonds between antibodies and the viral spike protein. In addition, the ability of antibodies to neutralise different SARS-CoV-2 variants in cell cultures plays a major role.

As the next step, therefore, the scientists compared the quantity and quality of antibodies and T cell responses to the spike protein among blood cancer patients and healthy study participants after two and three COVID-19 vaccinations. High-quality antibodies against different SARS-CoV-2 variants

The study revealed that patients who can form antibodies tend to produce antibodies of particularly high quality. After their second vaccination, they are already able to neutralise and thus deactivate different SARS-CoV-2 variants. This ability is considerably more pronounced in this patient cohort than in vaccinated healthy people.

"COVID-19 vaccination can generate very broad antiviral immunity -- including highly potent neutralising antibodies -- in patients with various types of blood cancer. Consequently, multiple vaccine doses can be recommended for patients with B-cell lymphoma or multiple myeloma without interrupting therapy," summarises Prof. Oliver T. Keppler.