More known unknowns
The tempered efficacy of the COVID-19 vaccines in patients with hematologic malignancies “has been shown in multiple studies of multiple myeloma, chronic lymphocytic leukemia (CLL), and other malignancies, and we know it’s true in transplant,” said Dr. Pergam.
In a study of 67 patients with hematologic malignancies at the University of Pittsburgh Medical Center Hillman Cancer Center, for instance, 46.3% did not generate IgG antibodies against the SARS-CoV-2 spike protein receptor–binding domain after completing their two-dose mRNA vaccine series. Patients with B-cell CLL were especially unlikely to develop antibodies.2A much larger study of more than 1,400 patients from investigators at the Mayo Clinics in Rochester, Minn., and Jacksonville, Fla., found that approximately 25% of all patients with hematologic malignancies did not produce antispike IgG antibodies, and that those with the most common B-cell malignancies had the lowest rate of seropositivity (44%-79%).3There’s a clear but challenging delineation between antibody testing in the research space and in clinical practice, however. Various national and cancer societies recommended earlier this year against routine postvaccine serological monitoring outside of clinical trials, and the sources interviewed for this story all emphasized that antibody titer measurements should not guide decisions about boosters or about the precautions advised for patients.
Titers checked at a single point in time do not capture the kinetics, multidimensional nature, or durability of an immune response, Dr. Warner said. “There are papers out there that say zero patients with CCL seroconverted … but they do still have some immunity, and maybe even a lot of immunity.”
Antibody testing can create a false sense of security, or a false sense of dread, he said. Yet in practice, the use of serological monitoring “has been all over the place [with] no consistency … and decisions probably being made at the individual clinic level or health system level,” he said.
To a lesser degree, so have definitions of what composes significant immunocompromise in the context of COVID-19 vaccine eligibility. “The question comes up, what does immunocompromised really mean?” said Dr. Yu, whose institution is a member of the Memorial Sloan Kettering (MSK) Cancer Alliance.
As of September, the MSK Cancer Center had taken a more granular approach to describing moderate to severe immunocompromise than did the Centers for Disease Control and Prevention. The CDC said this level of immunocompromise includes people receiving active cancer treatment for tumors or cancers of the blood, and those who’ve received a stem cell transplant within the past 2 years. MSK extended the recommendation, as it concerns hematologic malignancies, to patients who are within 12 months after treatment with B-cell depleting drugs, patients who have been treated for blood cancers within the last 6 months, and patients who received CAR T therapy within the past 2 years.
Dr. Yu, who was not involved in creating the MSK recommendations for third COVID-19 vaccines, said that he has been thinking more broadly during the pandemic about the notion of immunocompetence. “It’s my opinion that patients with hematologic malignancies, even if they’re not on treatment, are not fully immune competent,” he said. This includes patients with CLL stage 0 and patients with plasma cell dyscrasias who don’t yet meet the criteria for multiple myeloma but have a monoclonal gammopathy, and those with lower-risk myelodysplastic syndromes, he said.
“We’re seeing [variable] recommendations based on expert opinion, and I think that’s justifiable in such a dynamic situation,” Dr. Yu said. “I would [even] argue it’s desirable so we can learn from different approaches” and collect more rigorous observational data.
Immunocompetence needs to be “viewed in the context of the threat,” he added. “COVID changes the equation. … What’s immunocompromised in my mind has changed [from prepandemic times].”