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Responses to COVID-19 vaccines are likely to be blunted in HCT, or CAR T cell recipients compared with healthy individuals. The overall lower efficacy was thought to be due to the newly emerging SARS-CoV-2 variant arising from South Africa (20H/501Y.V2 variant ), which was the predominant strain circulating in South Africa at the time of the clinical trial, and accounted for 95 percent of the sequenced isolates. The single-dose recombinant, replication-incompetent adenovirus serotype 26 (Ad26) vector-based vaccine ( Johnson & Johnson/Janssen) reduced the incidence of symptomatic COVID-19 with a reported efficacy of 66.1 percent (72% in the United States) based on data from the phase III clinical trial. The BNT162b2 (Pfizer/BioNTech) and the mRNA-1273 (Moderna) COVID-19 vaccines have both been shown in large phase III clinical trials to be more than 90 percent effective at preventing lab-confirmed COVID-19 illness and severe infections. Food and Drug Administration (FDA) or are approved under the FDA’s Emergency Use Authorization (EUA).

In the United States, two novel messenger RNA (mRNA) vaccines and one novel adenovirus vector–based vaccine have been either formally approved by the U.S. These patients also face other comorbidities associated with COVID-19–related mortality, including older age, cardiovascular disease, renal dysfunction, and high-level immunosuppression, among many others that further deepen and drive worse outcomes. Hematopoietic cell transplant (HCT) and chimeric antigen receptor T (CAR T) cell recipients are at higher risk for serious complications from the virus, including hospitalization, intensive care unit admission, and death from COVID-19. The SARS-CoV-2 pandemic continues to cause excess morbidity and mortality in the United States and worldwide.

However, COVID-19 vaccines remain the cornerstone for prevention of severe illness, hospitalization, and death from SARS-CoV-2. Advances in therapeutics such as monoclonal antibodies for prevention and treatment of COVID-19 have become available and can be given irrespective of vaccination status. Our understanding of vaccine responses in immunocompromised patients has improved, leading to revised schedules and changes in the number of doses needed.

The changes reflect the access to new data the need to optimize vaccination uptake and timeline during new surges and the spread of new variants of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and the need to better protect vulnerable populations. Vaccination recommendations have been attuned since the first COVID-19 vaccines became available. Hohl, MD, PhD Mini Kamboj, MD Michael Boeckh, MD, PhD and Genovefa Papanicolaou, MD. Pergam, MD, MPH John Wingard, MD Jeffery Auletta, MD Zeinab El Boghdadly, MBBCh Maheen Abidi, MD Alpana Waghmare, MD Zainab Shahid, MD Laura Michaels, MD Joshua Hill, MD Tobias M. Chemaly, MD, MPH Sanjeet Dadwal, MD Steven A. Recent advances in culturing ES cells and success in exploiting their pluripotency brings great hope for using human ES cell-based reparative therapy in future.(Version 5.0 last updated March 22, 2022) On the basis of this property, it is likely that human ES cells will provide a useful differentiation culture system to study the mechanisms of human development. Data are now emerging that ES cells can be directed toward lineage-specific differentiation programs. Studies of development in model systems, such as mice help our efforts to manipulate human stem cells in vitro. Many scientific studies have tried to manipulate the growth and differentiation conditions with varied success. These cells have some special requirements to maintain their undifferentiated state in culture, e.g., presence of feeder cells, serum, or cytokines. To date, only three species of mammals have yielded long-term cultures of self-renewing ES cells- mice, monkeys, and humans. Embryonic stem (ES) cells have the ability to form any fully differentiated cell of the body.

Stem cells are unique cell populations with the ability to choose between self-renewal and differentiation.