Early CD8+-recovery independently predicts low probability of disease relapse but also associates with severe GVHD after allogeneic HSCT

Metrological traceability in flow cytometry? Evaluation of a new volumetric method for lymphocyte subsets

INTRODUCTION

Lymphocyte subset enumeration by flow cytometry is important for the therapeutic monitoring of a range of conditions. However, current bead-based methodologies do not produce metrologically traceable results. Here we compare an established bead-based methodology with a volumetric-based system traceable to an internationally recognised reference method.

METHOD

A total of 118 samples received for lymphocyte subset analysis were tested using an established bead-based technique (BD Multitest™ 6-colour TBNK assay using Trucount™ tubes on a BD FACSLyric flow cytometer), followed by a volumetric method on the Sysmex XF-1600 flow cytometer using Exbio Kombitest 6-colour TBNK reagent. All samples were tested in accordance with the manufacturer's instructions.

RESULTS

Absolute count values from both methodologies for CD3+, CD3 + CD4+, CD3 + CD8+, CD19+ and CD3-CD16+/CD56+ lymphocyte populations were compared using linear regression (R2 for all parameters >0.95) and Bland-Altman analysis. There was no significant bias (where p < 0.05) for absolute CD3 + CD4+ lymphocytes in the defined therapeutic range of 0-250 cells/μL (mean bias: 0.27 cells/μL). Although positive biases were seen for CD3 + CD4+ lymphocytes (over the entire range tested: 14-1798 cells/μL) and CD3-CD16+/CD56+ lymphocytes (mean bias: 10.83 cells/μL and 6.79 cells/μL, respectively). Negative biases were seen for CD3 + CD8+ and CD19+ lymphocytes (mean bias: -29.17 cells/μL and - 18.76 cells/μL, respectively).

CONCLUSION

A high degree of correlation was found for results from both methodologies and observed bias was within the limits of clinical acceptability for all populations. This shows that the metrologically traceable lymphocyte subset absolute counts produced by the Sysmex XF-1600 are robust within clinically required limits.

Persistent Impairment in Immune Reconstitution and Worse Survival Outcomes in Allogeneic Stem Cell Transplantation Patients with Early Coronavirus Disease 2019 Infection

Patients undergoing allogenic hematopoietic stem cell transplantation (HSCT) are at an increased risk of mortality due to transplantation-related complications in the first year post-transplantation, owing in part to the profound immune dysregulation with T cell and B cell lymphopenia and functional impairment. Although several large studies have reported higher mortality rates from Coronavirus disease 2019 (COVID-19) in HSCT recipients, to date no study has focused on the impact of early COVID-19 infection on immune reconstitution post-transplantation and the correlation with transplantation outcomes. We retrospectively analyzed 61 consecutive adult patients who underwent their first allogeneic HSCT at our institution. Thirteen patients (21.3%) experienced early COVID-19 infection, with a median time to diagnosis of 100 days post-transplantation. In multivariable analysis, patients with early COVID-19 infection had significantly worse overall survival (adjusted hazard ratio [aHR], 4.06; 95% confidence interval [CI], 1.26 to 13.05; P = .019) and progression-free survival (aHR, 6.68; 95% CI, 2.11 to 21.11; P = .001). This was attributed mainly to higher nonrelapse mortality (NRM) among early COVID-19 patients (P = .042). Allogeneic HSCT recipients with early COVID-19 infection had significant delays in absolute lymphocyte count (95% CI, -703.69 to -56.79; P = .021), CD3+CD4+ cell (95% CI, -105.35 to -11.59; P = .042), CD3+CD8+ cell (95% CI, -324.55 to -57.13; P = .038), and CD3-CD56+ cell (95% CI, -193.51 to -47.31; P = .014) recovery compared to those without early COVID-19 infection. Our findings suggest that patients with early COVID-19 infection after allogeneic HSCT have higher NRM and worse survival, at least in part due to impaired immune reconstitution post-transplantation.

The role of immune reconstitution in relapse after allogeneic hematopoietic stem cell transplantation

INTRODUCTION

Leukemia relapse following stem cell transplantation remains a significant barrier to long-term remission. Timely and balanced immune recovery after transplantation is crucial for preventing leukemia relapse.

AREAS COVERED

After an extensive literature search of PubMed and Web of Science through October 2023, we provide an overview of the dynamics of immune reconstitution and its role in controlling leukemia relapse. We also discuss strategies to promote immune reconstitution and reduce disease recurrence following allogeneic hematopoietic stem cell transplantation.

EXPERT OPINION

Immune reconstitution after transplantation has substantial potential to prevent relapse and might predict disease recurrence and prognosis. High dimensional cytometry, multi-omics, and T cell repertoire analysis allow for a more comprehensive and detailed understanding of the immune system's dynamics post-transplantation, and contribute to the identification of rare immune cell subsets or potential biomarkers associated with successful immune reconstitution or increased risk of complications. Strategies to enhance the immune system, such as adoptive immunotherapy and cytokine-based therapy, have great potential for reducing leukemia relapse after transplantation. Future research directions should focus on refining patient selection for these therapies, implementing appropriate and timely treatment, investigating combination approaches to maximize therapeutic outcomes, and achieving a robust graft-versus-leukemia (GVL) effect while minimizing graft-versus-host disease (GVHD) for optimal results.

The impact of different doses of antithymocyte globulin conditioning on immune reconstitution upon hematopoietic stem cell transplantation

INTRODUCTION

Anti-thymocyte globulin (ATG) is used prior to allogeneic hematopoietic stem cell transplantation (allo-HSCT) for graft-versus-host disease (GVHD) prophylaxis. Two different ATG doses (7.5 or 10 mg/kg) were evaluated in comparison with a group without ATG therapy.

METHODS

We retrospectively analyzed 132 patients who were transplanted with HSCT without ATG (non-ATG), or who received 7.5 mg/kg ATG (ATG-7.5) or 10 mg/kg ATG (ATG-10) prior to transplantation. The immune cells (CD3⁺CD4⁺ T cells, CD3⁺CD8⁺ T cells, CD19⁺ B cells and CD16⁺CD56⁺ NK cells) were examined in peripheral blood every three months post-HSCT for 12 months.

RESULTS

Compared with non-ATG group, combined ATG-7.5/ATG-10 groups had significantly lower CD3⁺CD4⁺ T cells and higher CD3⁺CD8⁺ T cells at 3, 6, 9, 12 months post-HSCT; thus, displaying a lower CD4/CD8 ratio in the ATG groups compared to non-ATG group. The ratio of CD19⁺ B cells was statistically lower (at 3rd month, p = .014; at 6th month, p = .025) in combined ATG-7.5/ATG-10 groups at 3 and 6 months post-HSCT, but not at 9 and 12 months after HSCT. The ratios of CD3⁺CD4⁺ T cells, CD3⁺CD8⁺ T cells, CD19⁺ B cells and CD16⁺CD56⁺ NK cells were similar between the ATG-7.5 and ATG-10 groups at all examined time points. The overall survival (OS), progression-free survival (PFS), relapse and acute GVHD (aGVHD) were comparable among recipients without ATG therapy and with ATG-7.5 or/and ATG-10 therapies. Multivariate analysis revealed that immune cells ratios were not independent factors affecting prognosis.

CONCLUSION

The ATG therapy at higher and lower doses led to a delayed reconstitution of T cells and the inversion of CD4/CD8 ratio for at least one year after HSCT.

Outcomes of Adolescents and Young Adults Compared with Children with Acute Leukemia after Single-Unit Unrelated Cord Blood Transplantation Using Myeloablative Conditioning without Antithymocyte Globulin

BACKGROUND

Although the use of cord blood transplantation (CBT) is becoming more frequent in acute leukemia, considering the relationship between the low stem cell dose and graft failure, whether use of CBT for adolescents and young adults (AYAs) is appropriate remains uncertain.

METHODS

A retrospective registry-based analysis of clinical outcomes and immune reconstitution was conducted for 105 AYAs and 187 children with acute leukemia who underwent single-unit CBT using myeloablative conditioning (MAC) without antithymocyte globulin (ATG).

RESULTS

Outcomes were similar between AYAs and children, except for nonrelapse mortality (NRM) and recovery rates of neutrophils and platelets. The 30-day cumulative incidence of neutrophil engraftment was similar between AYAs and children, but children had faster rates of neutrophil and platelet recovery than AYAs. The median time to neutrophil engraftment was earlier in children than in AYAs (AYAs, 19 days, 95% confidence interval [CI] 17.3-21.7; children, 16 days, 95% CI 13.1-19.5, p = 0.00003). The incidence of platelet recovery on day 120 was higher in children than in AYAs (AYAs, 80%, 95% CI 71-81%; children, 88%, 95% CI 82-92%, p = 0.037). CD34+ cell dose was the only independent factor influencing both neutrophil and platelet recovery. The cumulative incidence of NRM at 2 years was higher among AYAs than among children (AYAs, 27.5%, 95% CI 20-37%; children, 15%, 95% CI 10-21%, p = 0.008). Conditioning regimen was an independent factor influencing NRM. With respect to immune reconstitution, natural killer cell counts quickly recovered to normal levels 1-month post-CBT in both children and AYAs. CD8+ T-cell counts were higher in children than in AYAs at 1 and 3 months post-CBT. CD4+ T-cell counts were similar in both children and AYAs after CBT.

CONCLUSION

AYAs with acute leukemia have outcomes of single-unit CBT using MAC without ATG that are as good as those of children. Thus, single-unit CBT using modified MAC without ATG is an acceptable choice for both AYAs and children who do not have a suitable donor.

High expression of granzyme B in conventional CD4+ T cells is associated with increased relapses after allogeneic stem cells transplantation in patients with hematological malignancies

Granzyme B is known to be a serine protease contained in granules of cytotoxic T cells. We have previously reported an influence of granzyme B expression in T regulatory cells (Tregs) on the risk of acute graft versus host disease (GVHD) onset. However, it is still unknown if conventional T cells (Tcon) use the granzyme B pathway as a mechanism of alloimmunity. We hypothesized that granzyme B in Tcon may affect recurrence within the first 6 months after allogeneic transplantation (allo-HSCT). A total of 65 patients with different hematological malignancies were included in this study. Blood samples were collected on day +30 after allo-HSCT. The percentage of granzyme B positive conventional T cells in patients who developed relapse in the first 6 months after allo-HSCT was 11.3 (4.5-35.3) compared to the others in continuous complete remission-1.3 (3.65-9.7), р = 0.011. The risk of relapse after allo-HSCT was in 3.9 times higher in patients with an increased percentage of granzyme B positive conventional T cells. The findings demonstrated that the percentage of granzyme B positive conventional T cells on day +30 after allo-HSCT could be a predictable marker of relapse within the first 6 months after allo-HSCT.