Immunogenicity of Pfizer mRNA COVID-19 Vaccination Followed by J&J Adenovirus COVID-19 Vaccination in Two Patients with Chronic Lymphocytic Leukemia.

Individuals with chronic lymphocytic leukemia (CLL) have significant immune disfunction, often further disrupted by treatment. While currently available COVID-19 vaccinations are highly effective in immunocompetent individuals, they are often poorly immunogenic in CLL patients. It is important to understand the role a heterologous boost would have in patients who did not respond to the initial two-dose mRNA vaccine series. SARS-CoV-2 specific immune responses, including antibodies and memory B-cells, CD4 and CD8 T-cells were assessed prior to vaccination, as well as postinitial vaccination series and post-third dose in two subjects. One subject seroconverted, had RBD-specific memory B-cells and spike-specific CD4 T-cells while the other did not. Both subjects had a spike-specific CD8 T-cell response after the original mRNA vaccination series that was further boosted after the third dose or remained stable. The results of this study, however small, are especially promising to CLL individuals who did not seroconvert following the initial mRNA vaccination series.

Cytokine-mediated programmed proliferation of virus-specific CD8(+) memory T cells.

During infection, CD8(+) T cells not only respond to antigenic signals through their T cell receptor (TCR) but also incorporate inflammatory signals from cytokines produced in the local infected microenvironment. Transient TCR-mediated stimulation will result in programmed proliferation that continues despite removal of the antigenic stimulus, but it remains unclear whether brief exposure to specific cytokines will elicit similar effects. Here, we have demonstrated that brief stimulation of memory T cells with interleukin-12 (IL-12) and interleukin-18 (IL-18) results in tightly regulated programmed proliferation, in addition to acquisition of enhanced virus-specific cytokine production and cytolytic activity. CD8(+) T cells briefly exposed to IL-12 and IL-18 in vitro showed improved antiviral activity in vivo, as demonstrated by increased proliferation and reduced viremia. These results indicate that even transitory exposure to inflammatory cytokines can provide a selective advantage to infiltrating CD8(+) T cells by triggering a developmental program that is initiated prior to direct contact with virus-infected cells.

Pivotal advance: CTLA-4+ T cells exhibit normal antiviral functions during acute viral infection.

Previous studies have shown that T cells, which are genetically deficient in CTLA-4/CD152 expression, will proliferate uncontrollably, resulting in lethal autoimmune disease. This and other evidence indicate that CTLA-4 plays a critical role in the negative regulation of effector T cell function. In contrast to expectations, BrdU incorporation experiments demonstrated that CTLA-4 expression was associated with normal or even enhanced in vivo proliferation of virus-specific CD4+ and CD8+ T cells following acute lymphocytic choriomeningitis virus or vaccinia virus infection. When compared with CTLA-4- T cells directly ex vivo, CTLA-4+ T cells also exhibited normal antiviral effector functions following stimulation with peptide-coated cells, virus-infected cells, plate-bound anti-CD3/anti-CTLA-4, or the cytokines IL-12 and IL-18. Together, this indicates that CTLA-4 does not directly inhibit antiviral T cell expansion or T cell effector functions, at least not under the normal physiological conditions associated with either of these two acute viral infections.