COVID‐19 systematic screening of asymptomatic haematopoietic stem cell donors: Less if often more

Abstract From COVID pandemic spread until now, many HSCT unrelated donor registries recommend as a precaution a systematic COVID‐19 testing for all donors during the precollection time. Literature is quite poor to support this systematic attitude. We report one sibling allogeneic HSCT which we proceeded despite a positive COVID test on related asymptomatic donor and summarize the all seven cases reported until now. We suggest to question this systematic COVID testing, two years after pandemic began, when there is no systematic testing on other blood products received during all the haematological malignancies treatment process.


INTRODUCTION
COVID-19 pandemic has disrupted care access for many patients around the world, including those requiring haematopoietic stem cell transplantation (HSCT). Respiratory route was demonstrated as the most common way of transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) [1]. Blood transmission is largely less documented. Viremia is indeed rarely described in asymptomatic patients tested positive for SARS-CoV-2 in nasopharyngeal sample but has been reported in patients presenting respiratory symptoms [2]. stem cell (HSC) donors before starting mobilization and before donation was introduced in routine practice for some registries. According to these registries guidelines, positivity of one of these samples theoretically contraindicates the HSC collection [3]. In our structure, since the beginning of the pandemic, we have implemented cryopreservation of the stem cell product, to be able to defer conditioning of the recipient, in order to arrange the collection of a back-up donor if necessary.
However, the donation delay and/or the use of an alternative donor can represent a real loss of chance for the recipient.

CASE REPORT
We report here the case of a 35-year-old female diagnosed with acute myeloid leukemia with normal karyotype and NPM1 mutation

DISCUSSION
More than 2 years after the beginning of the pandemic, it seems legiti- Numerous patients have received blood products (whole blood or platelets) from donors found to be positive in the days following donation: no transmission was observed [9]. Even immunocompromised patients did not develop symptoms after receiving blood products from infected donors [10]. These results suggest that the risk of blood transmission of the virus is low. In some countries, HSC donors are not tested for SARS-CoV-2 if they are asymptomatic, and cryopreservation is no longer recommended [11]. Indeed, several stem cell products have been cryopreserved but will likely never be infused. In our center, systematic cryopreservation is still the go-to procedure for HSCT (for both related and unrelated donor). This strategy was chosen to have time to launch the recruitment process of a back-up donor if the first one is contraindicated tardily.
Our observation, taken together with previously reported cases, raises new questions. With the current vaccination coverage and the very low viremia observed in asymptomatic patients [2], should screening guidelines evolve? Is cryopreservation still relevant for related donors and unrelated donors coming from countries with fast, easy and safe transport of the graft? Also, one can wonder about the impact of a "second choice" donor on the becoming of the transplant: is it better to proceed with the apheresis of the best donor, infected but asymptomatic or to turn to the back-up donor?
The COVID-19 pandemic is still here, and we will have to learn

CONFLICT OF INTEREST
The authors declare they have no conflicts of interest.

FUNDING INFORMATION
The authors received no specific funding for this work.

DATA AVAILABILITY STATEMENT
The data that support the findings of this study are available upon request from the corresponding author.

ETHIC STATEMENT
This work is integrally included in patient care. Both donor and patient have signed a written consent form relative to the use of biological material and data.