Total platelet donation count and donation frequency are determinants of plateletpheresis-associated lymphopenia

Comparative evaluation of hematological parameters and instrument performance in single and double plateletpheresis procedures using Haemonetics MCS+ and Trima Accel systems

OBJECTIVES

Plateletpheresis (PP) has become increasingly prevalent due to its cost-effectiveness and fewer immunological and infectious complications for recipients. This study compares hematological indices of platelet donors and instrument-related parameters in high-yield PP donors using Haemonetics MCS+ and Trima Accel.

METHODS

Eligible and healthy PP donors meeting the platelet donation criteria were randomly selected.19 single-dose platelet (SDP), and 26 double-dose platelet (DDP) donors underwent PP using the Haemonetics MCS+, while 21 SDP and 21 DDP donors were processed using the Trima Accel system. Complete Blood Count (CBC) and hematological indices of donors between groups with both devices were measured with the cell counter. Platelet yield, collection efficiency (CE), and collection rate (CR) were evaluated for both devices. Results were reported using R-4.3.2 software and a p-value <0.05 was considered statistically significant.

RESULTS

The Trima Accel processed significantly more blood volume and had shorter procedure times than MCS+. Platelet yield in the SDP group with Trima Accel was significantly higher than the Haemonetics MCS+. The Trima Accel demonstrated a significantly higher CR and CE than the MCS+ in both SDP and DDP groups. Post-PP lymphocyte counts significantly decreased with the Trima compared to the MCS+ in the SDP group. However, post-PP hematocrit (HCT), mean corpuscular volume (MCV), and mean platelet volume (MPV) in the DDP group with the MCS+ were significantly lower than Trima.

CONCLUSION

Double-dose plateletpheresis (DDP) offers advantages in cost-effectiveness and platelet production, and although it reduces some hematological indices, these remain within normal limits. The Trima Accel may offer superior efficiency and processing times compared to the MCS+. However, careful monitoring of DDP donors following AABB standards remains essential.

Effect of the added plasma rinseback on residual cell types in plateletpheresis leukoreduction systems

BACKGROUND

Platelets collected by the Trima Accel apheresis device (Terumo BCT) are automatically leukoreduced through a leukoreduction system (LRS) where WBCs are trapped in a conical-shaped LRS chamber. The content has been used as a valuable source of mononuclear cells for research purposes. In frequent, long-term platelet apheresis donors, lymphopenia has been associated with the use of LRS chambers, and implementation of plasma rinseback at the end of the procedure has been shown to mitigate the depletion of lymphocytes. In this report, the cellular content of the LRS chamber and remaining disposable was characterized with and without plasma rinseback.

STUDY DESIGN AND METHODS

Trima disposable sets were obtained from apheresis platelet collections in 100% plasma or 35% plasma/65% PAS with or without plasma rinseback at the end of the collections. Cellular content was drained from the LRS chamber and the disposable and was characterized using a hematology analyzer and flow cytometer to establish total cell counts and proportions of RBC, platelet, and WBC subpopulations.

RESULTS

LRS chambers contained approximately 109 WBCs, with the majority being lymphocytes and monocytes. The addition of plasma rinseback significantly decreased the number of WBCs remaining in the disposable, thereby increasing the number of WBCs returned to the donor. However, rinseback did not impact the WBC content of the LRS chamber itself.

CONCLUSIONS

Blood Centers using the Trima Accel instrument may reduce lymphopenia in regular platelet donors by implementing plasma rinseback, while ensuring the cellular content of the LRS chamber intended for research purposes remains unaffected.

T-cell lymphopenia in frequent volunteer platelet donors

In the United States, more than 2 000 000 apheresis platelet units are collected annually from volunteer donors. Platelet donors in the United States and elsewhere are permitted to donate up to 24 times per year. Recently, frequent apheresis platelet donation has been associated with severe T-cell lymphopenia. Several frequent platelet donors have been found to have peripheral blood CD4+ T-cell counts below 200 cells/µL, the threshold for AIDS in HIV-positive individuals. Independent risk factors for plateletpheresis-associated lymphopenia include lifetime donations, age, and donations on the Trima Accel instrument (Terumo BCT), which uses a leukoreduction system (LRS) chamber to trap white blood cells. Less often, severe lymphopenia can occur in donors collected on the Fenwal Amicus instrument (Fresenius Kabi), which has no LRS. For Trima Accel donors, lymphopenia can be partially mitigated by performing a plasma rinseback step at the end of collection. To date, there is no definitive evidence that plateletpheresis-associated lymphopenia is harmful. In a study of frequent platelet donors with lymphopenia who were administered COVID-19 messenger RNA vaccines, immune responses were normal. The homeostatic mechanisms responsible for maintaining a normal peripheral blood T-cell count remain obscure, as do the causal mechanisms underlying plateletpheresis-associated lymphopenia.

Risk factors for T-cell lymphopenia in frequent platelet donors: The BEST collaborative study

BACKGROUND

Severe T-cell lymphopenia of uncertain clinical significance has been observed in frequent apheresis platelet donors. Two commonly used plateletpheresis instruments are the Trima Accel, which uses a leukoreduction system (LRS) chamber to trap leukocytes and the Fenwal Amicus, which does not use an LRS chamber.

STUDY DESIGN AND METHODS

We performed an international, multicenter, observational study comparing T-cell populations in frequent platelet donors collected exclusively using the Trima instrument (n = 131) or the Amicus instrument (n = 77). Age- and sex-matched whole blood donors (n = 126) served as controls.

RESULTS

CD4+ T-cell counts <200 cells/μL were found in 9.9% of frequent Trima (LRS+) platelet donors, 4.4% of frequent Amicus (LRS-) platelet donors, and 0 whole blood donors (p < .0001). CD4+ T-cell counts <200 cells/μL were only seen in platelet donors with ≥200 lifetime donations. In multivariable analysis, age, lifetime donations, and instrument (Trima vs. Amicus) were independent risk factors for lymphopenia. In 40 Trima platelet donors, a plasma rinseback procedure was routinely performed following platelet collections. No Trima platelet donors receiving plasma rinseback had a CD4+ T-cell count <200 cells/μL versus 13/91 Trima platelet donors not receiving plasma rinseback (p = .01).

DISCUSSION

Recurrent bulk lymphocyte removal appears to contribute to the development of T-cell lymphopenia in frequent, long-term platelet donors. Lymphopenia is more common when an LRS chamber is used during platelet collection but can occur without an LRS chamber. Blood centers using LRS chambers can mitigate donor lymphopenia by performing plasma rinseback.

Duties to donors

See article on page 2072–2082, in this issue

COVID-19 vaccine humoral response in frequent platelet donors with plateletpheresis-associated lymphopenia

BACKGROUND

Plateletpheresis involves platelet separation and collection from whole blood while other blood cells are returned to the donor. Because platelets are replaced faster than red blood cells, as many as 24 donations can be done annually. However, some frequent apheresis platelet donors (>20 donations annually) display severe plateletpheresis-associated lymphopenia; in particular, CD4+ T but not B cell numbers are decreased. COVID-19 vaccination thereby provides a model to assess whether lymphopenic platelet donors present compromised humoral immune responses.

STUDY DESIGN AND METHODS

We assessed vaccine responses following 2 doses of COVID-19 vaccination in a cohort of 43 plateletpheresis donors with a range of pre-vaccination CD4+ T cell counts (76-1537 cells/μl). In addition to baseline T cell measurements, antibody binding assays to full-length Spike and the Receptor Binding Domain (RBD) were performed pre- and post-vaccination. Furthermore, pseudo-particle neutralization and antibody-dependent cellular cytotoxicity assays were conducted to measure antibody functionality.

RESULTS

Participants were stratified into two groups: <400 CD4/μl (n = 27) and ≥ 400 CD4/μl (n = 16). Following the first dose, 79% seroconverted within the <400 CD4/μl group compared to 87% in the ≥400 CD4/μl group; all donors were seropositive post-second dose with significant increases in antibody levels. Importantly differences in CD4+ T cell levels minimally impacted neutralization, Spike recognition, and IgG Fc-mediated effector functions.

DISCUSSION

Overall, our results indicate that lymphopenic plateletpheresis donors do not exhibit significant immune dysfunction; they have retained the T and B cell functionality necessary for potent antibody responses after vaccination.