Differences inAspergillus-specific immune recovery between T-cell-replete and T-cell-depleted hematopoietic transplants

Contemporary analysis of functional immune recovery to opportunistic and vaccine-preventable infections after allogeneic haemopoietic stem cell transplantation

Objectives

Infections are a major cause of mortality after allogeneic haemopoietic stem cell transplantation (alloHSCT), and immune recovery is necessary for prevention. Novel transplant procedures have changed the epidemiology of infections but contemporary data on functional immune recovery are limited. In this pilot study, we aimed to measure immune recovery in the current era of alloHSCT.

Methods

Twenty, 13, 11, 9 and 9 alloHSCT recipients had blood collected at baseline (time of conditioning) and 3‐, 6‐, 9‐, and 12‐months post‐alloHSCT, respectively. Clinical data were collected, and immune recovery was measured using immunophenotyping, lymphocyte proliferation, cytokine analysis and antibody isotyping.

Results

Median absolute T‐ and B‐cell counts were below normal from baseline until 9‐ to 12‐months post‐alloHSCT. Median absolute CD4⁺ T‐cell counts recovered at 12‐months post‐alloHSCT. Positive proliferative responses to Aspergillus, cytomegalovirus (CMV), Epstein‐Barr virus (EBV), influenza and tetanus antigens were detected from 9 months. IL‐6 was the most abundant cytokine in cell cultures. In cultures stimulated with CMV, EBV, influenza and tetanus peptides, the CD4⁺ T‐cell count correlated with IL‐1β (P = 0.045) and CD8⁺ T‐cell count with IFNγ (P = 0.013) and IL‐1β (P = 0.012). The NK‐cell count correlated with IL‐1β (P = 0.02) and IL‐17a (P = 0.03). Median serum levels of IgG1, IgG2 and IgG3 were normal while IgG4 and IgA were below normal range throughout follow‐up.

Conclusions

This pilot study demonstrates that immune recovery can be measured using CD4⁺ T‐cell counts, in vitro antigen stimulation and selected cytokines (IFNγ, IL‐1β, IL‐4, IL‐6, IL‐17, IL‐21, IL‐31) in alloHSCT recipients. While larger studies are required, monitoring immune recovery may have utility in predicting infection risk post‐alloHSCT.

High Incidence of Early Human Herpesvirus-6 Infection in Children Undergoing Haploidentical Manipulated Stem Cell Transplantation for Hematologic Malignancies

Human herpesvirus-6 (HHV-6) infection is increasingly recognized among allogeneic hematopoietic stem cell transplantation (HSCT) recipients, with 30% at risk of reactivation in the haploidentical setting. It has been associated with encephalitis, acute graft-versus-host disease, and graft failure. Here we report 2 cohorts of pediatric haploidentical manipulated HSCT in which, despite many differences, HHV-6 reactivation and disease occurred with very high incidence compared with data reported in the literature and represented the main early post-transplant infectious complication compared with other viral, bacterial, or fungal infections. The 2 cohorts were recruited at the pediatric transplant centers of Perugia (n = 13), Barcelona (n = 10), and Madrid (n = 15). All patients received myeloablative conditioning regimens and 2 different types of ex vivo graft manipulation: CD34⁺ selection and regulatory T cell/conventional T cell infusion in 13 patients and CD45RA T cell depletion in 25 patients. Antiviral prophylaxis was acyclovir in 33 and foscarnet in 5 patients. HHV-6 DNAemia was checked by quantitative or qualitative PCR. In vitro experiments demonstrated that donor CD4⁺ T cells are the reservoir of HHV-6 and suggested a role of the graft composition in both transplant settings (rich in CD4⁺ T cells) in the high rate of HHV-6 infections. All patients presented very early HHV-6 DNAemia after transplantation, and although viremic, 9 patients (24%) developed symptomatic limbic encephalitis. All patients responded to antiviral treatment, and none died of infection, although 2 experienced long-term neurologic sequelae (22%). Moreover, 6 patients presented organ involvement in absence of other causes: 1 hepatitis, 1 pneumonia, 2 gastroenteritis, and 2 multiorgan involvement(1 encephalitis, pneumonia, and gastritis; 1 pneumonia and enteritis). Incidences of other viral, bacterial, and fungal diseases were lower in both cohorts. In vitro, HHV-6 was found to infect only CD4⁺ fraction of the graft. Co-culturing CD4⁺ T cells with CD56⁺ natural killer (NK) cells eliminated the virus, demonstrating the main role of NK cells in the antiviral immune response. All 38 pediatric patients undergoing these manipulated haploidentical HSCTs showed HHV-6 reactivation, and 14 of 38 developed HHV-6 disease with similar features in terms of timing, morbidity, response to treatment, and outcome. The graft composition in both transplant platforms, rich in CD4⁺ T cells and poor in NK cells, seems to play a key role. HHV-6 DNAemia surveillance was useful to diagnose and treat preemptively HHV-6 infection.

Modulating host immune responses to fight invasive fungal infections

Modulation of host immunity in invasive fungal infection is an appealing but as yet mostly elusive treatment strategy. Animal studies in invasive candidiasis and aspergillosis have demonstrated beneficial effects of colony stimulating factors, interferon-gamma and monoclonal antibodies. More recent studies transfusing leukocytes pre-loaded with lipophilic anti-fungal drugs, or modulated T-cells, along with novel vaccination strategies show great promise. The translation of immune therapies into clinical studies has been limited to date but this is changing and the results of new Candida vaccine trials are eagerly awaited. Immune modulation in HIV-associated mycoses remains complicated by the risk of immune reconstitution inflammatory syndrome and although exogenous interferon-gamma therapy may be beneficial in cryptococcal meningitis, early initiation of anti-retroviral therapy leads to increased mortality. Further study is required to better target protective immune responses.

Adoptive transfer of Aspergillus-specific T cells as a novel anti-fungal therapy for hematopoietic stem cell transplant recipients: Progress and challenges

Although newer antifungal drugs have substantially altered the natural history of invasive aspergillosis, the disease still accounts for significant morbidity and mortality in hematopoietic stem cell transplant recipients. Both the evidence supporting a protective role of T cells against this fungal pathogen and the documented efficacy of adoptive transfer of antigen-specific T cells for prophylaxis and treatment of viral infections post-transplant have stimulated much interest towards development of Aspergillus-specific T cells (Asp-STs) for adoptive immunotherapy in the allogeneic transplant setting. In contrast to the remarkable progress with virus-specific T cells, clinical development of fungus-specific T cells is still in its infancy. Several groups have characterized Asp-STs in healthy individuals and patients with malignant hematological diseases, while others sought to develop GMP-compliant methods of expanding or bioengineering Asp-STs ex vivo as immunotherapy. This review highlights the recent advances in this field, and discusses critical issues involved in development and protocol design of Asp-ST immunotherapy.