Adriana S. Albuquerque

First use of thymus transplantation therapy for FOXN1 deficiency (nude/SCID): a report of 2 cases.

FOXN1 deficiency is a primary immunodeficiency characterized by athymia, alopecia totalis, and nail dystrophy. Two infants with FOXN1 deficiency were transplanted with cultured postnatal thymus tissue. Subject 1 presented with disseminated Bacillus Calmette-Guérin infection and oligoclonal T cells with no naive markers. Subject 2 had respiratory failure, human herpes virus 6 infection, cytopenias, and no circulating T cells. The subjects were given thymus transplants at 14 and 9 months of life, respectively. Subject 1 received immunosuppression before and for 10 months after transplantation. With follow up of 4.9 and 2.9 years, subjects 1 and 2 are well without infectious complications. The pretransplantation mycobacterial disease in subject 1 and cytopenias in subject 2 resolved. Subject 2 developed autoimmune thyroid disease 1.6 years after transplantation. Both subjects developed functional immunity. Subjects 1 and 2 have 1053/mm(3) and 1232/mm(3) CD3(+) cells, 647/mm(3) and 868/mm(3) CD4(+) T cells, 213/mm(3) and 425/mm(3) naive CD4(+) T cells, and 10 200 and 5700 T-cell receptor rearrangement excision circles per 100 000 CD3(+) cells, respectively. They have normal CD4 T-cell receptor β variable repertoires. Both subjects developed antigen-specific proliferative responses and have discontinued immunoglobulin replacement. In summary, thymus transplantation led to T-cell reconstitution and function in these FOXN1 deficient infants.

Rate of Increase in Circulating IL-7 and Loss of IL-7Rα Expression Differ in HIV-1 and HIV-2 Infections: Two Lymphopenic Diseases with Similar Hyperimmune Activation but Distinct Outcomes

IL-7 is a nonredundant cytokine for T cell homeostasis. Circulating IL-7 levels increase in lymphopenic clinical settings, including HIV-1 infection. HIV-2 infection is considered a “natural” model of attenuated HIV disease given its much slower rate of CD4 decline than HIV-1 and limited impact on the survival of the majority of infected adults. We compared untreated HIV-1- and HIV-2-infected patients and found that the HIV-2 cohort demonstrated a delayed increase in IL-7 levels during the progressive depletion of circulating CD4 T cells as well as a dissociation between the acquisition of markers of T cell effector differentiation and the loss of IL-7Rα expression. This comparison of two persistent infections associated with progressive CD4 depletion and immune activation demonstrates that a better prognosis is not necessarily associated with higher levels of IL-7. Moreover, the delayed increase in IL-7 coupled with sustained expression of IL-7Rα suggests a maximization of available resources in HIV-2. The observation that increased IL-7 levels early in HIV-1 infection were unable to reduce the rate of CD4 loss and the impaired expression of the IL-7Rα irrespective of the state of cell differentiation raises concerns regarding the use of IL-7 therapy in HIV-1 infection.

Increased Frequency of Circulating CCR5+ CD4+ T Cells in Human Immunodeficiency Virus Type 2 Infection

ABSTRACT CCR5 expression determines susceptibility to infection, cell tropism, and the rate of human immunodeficiency virus type 1 (HIV-1) disease progression. CCR5 is also considered the major HIV-2 coreceptor in vivo, in spite of broad coreceptor use in vitro. Here we report a significantly increased proportion of memory-effector CD4 T cells expressing CCR5 in HIV-2-infected patients correlating with CD4 depletion. Moreover, HIV-2 proviral DNA was essentially restricted to memory-effector CD4, suggesting that this is the main target for HIV-2. Similar levels of proviral DNA were found in the two infection categories. Thus, the reduced viremia and slow rate of CD4 decline that characterize HIV-2 infection seem to be unrelated to coreceptor availability.

Human FOXN1-deficiency is associated with αβ double-negative and FoxP3+ T-cell expansions that are distinctly modulated upon thymic transplantation.

Forkhead box N1 (FOXN1) is a transcription factor crucial for thymic epithelium development and prevention of its involution. Investigation of a patient with a rare homozygous FOXN1 mutation (R255X), leading to alopecia universalis and thymus aplasia, unexpectedly revealed non-maternal circulating T-cells, and, strikingly, large numbers of aberrant double-negative αβ T-cells (CD4negCD8neg, DN) and regulatory-like T-cells. These data raise the possibility that a thymic rudiment persisted, allowing T-cell development, albeit with disturbances in positive/negative selection, as suggested by DN and FoxP3+ cell expansions. Although regulatory-like T-cell numbers normalized following HLA-mismatched thymic transplantation, the αβDN subset persisted 5 years post-transplantation. Involution of thymus allograft likely occurred 3 years post-transplantation based on sj/βTREC ratio, which estimates intrathymic precursor T-cell divisions and, consequently, thymic explant output. Nevertheless, functional immune-competence was sustained, providing new insights for the design of immunological reconstitution strategies based on thymic transplantation, with potential applications in other clinical settings.

Monocyte-mediated T cell suppression by HIV-2 envelope proteins

HIV‐2 is associated with an attenuated form of HIV disease. We investigate here the immunosuppressive effects of the HIV‐2 envelope protein, gp105. We found that gp105 suppresses activation of T cells through a monocyte‐mediated mechanism. Suppression of T cell activation by gp105 depends on contact between monocytes and T cells, but not on CD4+CD25+ T cells. The TLR4 pathway is likely involved, since gp105 activates TLR4 signaling and induces TNF‐α production by monocytes. Immunosuppression is viewed as the main pathophysiologic consequence of infection by HIV. However, the main immunologic defect caused by HIV, depletion of T cells, requires T cell activation. Our findings are consistent with a new concept that HIV‐2 envelope proteins act on monocytes to suppress T cell activation and that this property may contribute to the benign course of HIV‐2. We hypothesize that the HIV‐2 envelope immunosuppressive properties limit bursts of T cell activation, thus reducing viremia and contributing to the slow rate of disease progression that characterizes HIV‐2 disease.

Memory and naive-like regulatory CD4+ T cells expand during HIV-2 infection in direct association with CD4+ T-cell depletion irrespectively of viremia

Objective:The dynamics of CD4+ regulatory T cells (Treg) during HIV-1 infection remains unclear. To further investigate Treg in this context, we characterized, for the first time, this population in HIV-2-positive individuals. Although both HIV infections are associated with hyperimmune activation and CD4+ T-cell lymphopenia, most HIV-2-positive individuals display slower disease progression and low-to-undetectable viremia. Design/methods:Samples were obtained from cohorts of untreated HIV-2-positive and HIV-1-positive, treated HIV-1-positive and seronegative individuals. The proportion of CD4+ T cells bearing a Treg phenotype, defined in terms of high-level CD25 or Foxp3 expression, was assessed by flow cytometry and correlated with markers of disease progression. The proportions of naive and memory-like subsets as well as cycling cells were determined. Results:We observed an increased proportion of Treg, associated with disease progression, as well as increased proportions of cycling (Ki67+) memory Treg, in untreated HIV-2-positive and HIV-1-positive individuals. We also noted an expansion of Treg that persisted over time in treated, immunologically discordant HIV-1-positive individuals, who, similarly to HIV-2-positive patients, present undetectable viremia and low CD4 T-cell count. Conclusion:Overall, we demonstrated that Treg frequency was increased in all lymphopenic HIV-2-positive and HIV-1-positive individuals irrespective of the presence or absence of viremia or antiretroviral treatment. This, in turn, suggests that the observed alterations in Treg frequency in HIV/AIDS are more directly related to the degree of CD4 depletion than to viremia.

Long-Term Immune Reconstitution of Naive and Memory T Cell Pools after Haploidentical Hematopoietic Stem Cell Transplantation

Haploidentical hematopoietic stem cell transplantation (HSCT) constitutes an important alternative for patients lacking a human leukocyte antigen (HLA)-matched donor. Although the use of haploidentical donors is increasingly common, the long-term impact of generating a donor-derived immune system in the context of an HLA-mismatched thymic environment remains poorly characterized. We performed an in-depth assessment of immune reconstitution in a group of haploidentical HSCT recipients 4 to 6 years posttransplantation, in parallel with the respective parental donors and age-matched healthy control subjects. Our data show that the proportion of naive and memory subsets in the recipients, both within CD8(+) and CD4(+) T cells, more closely resembled that observed in age-matched control subjects than in the donors. HSCT recipients displayed relatively high signal-joint T cell-receptor excision circle levels and a high frequency of the recent thymic emigrant-enriched CD31(+) subset within naive CD4(+) and naive regulatory T cells. Moreover, CD8(+), CD4(+), and regulatory T cells from HSCT recipients displayed a diverse T cell repertoire. These results support a key role for thymic output in T cell reconstitution. Nevertheless, HSCT recipients had significantly shorter telomeres within a naive-enriched CD4(+) T cell population than age-matched control subjects, despite the similar telomere length observed within the most differentiated CD8(+) and CD4(+) T cell subsets. Overall, our data suggest that long-term immune reconstitution was successfully achieved after haploidentical HSCT, a process that appears to have largely relied on de novo T cell production.

Increased frequency of CD25dimCD4+ T-cells in HIV-2 infection, a naturally occurring attenuated form of HIV-1.

The ability to maintain the CD4-memory pool is currently considered one of the main determinants of AIDS progression. Like HIV-1, HIV-2 infection is characterized by progressive hyper-immune activation, yet it is associated with slower rates of CD4-loss and reduced viremia irrespective of disease stage. In contrast to HIV-1, we observed an increased proportion of CD4(+) T-cells expressing CD25 in HIV-2 infected individuals, independent of the degree of CD4-depletion and levels of immune activation. This was due to CD4(+) T-cells expressing an intermediate intensity of CD25, characterized by an increased ability to produce IL-2 and a lack of other regulatory markers. This expansion, unique to HIV-2 seropositive individuals, may relate to an improved ability to replenish their CD4-memory pool, and thus to the better prognosis that characterizes HIV-2 infection. Identification of the underlying mechanisms regulating this population in HIV-1 and HIV-2 infections may provide a rational for novel therapeutic strategies.

Autoimmunity and allergy control in adults submitted to complete thymectomy early in infancy

The contribution of the decline in thymic activity for the emergence of autoimmunity is still debatable. Immune-competent adults submitted to complete thymectomy early in life provide a unique model to address this question. We applied here strict criteria to identify adults lacking thymic activity based on sjTREC levels, to exclude thymic rebound and/or ectopic thymuses. In agreement, they featured severe naïve CD4 T-cell depletion and contraction of T-cell receptor diversity. Notwithstanding this, there was neither increased incidence of autoimmune disease in comparison with age-matched controls nor significant changes in their IgG/IgA/IgM/IgE autoreactivity profiles, as assessed through extensive arrays. We reasoned that the observed relative preservation of the regulatory T-cell compartment, including maintenance of naïve regulatory CD4 T-cells, may contribute to limit the emergence of autoimmunity upon thymectomy. Our findings have implications in other clinical settings with impaired thymic activity, and are particularly relevant to studies of autoimmunity in ageing.

IL-7-Induced Proliferation of Human Naive CD4 T-Cells Relies on Continued Thymic Activity

Naive CD4 T-cell maintenance is critical for immune competence. We investigated here the fine-tuning of homeostatic mechanisms of the naive compartment to counteract the loss of de novo CD4 T-cell generation. Adults thymectomized in early childhood during corrective cardiac surgery were grouped based on presence or absence of thymopoiesis and compared with age-matched controls. We found that the preservation of the CD31− subset was independent of the thymus and that its size is tightly controlled by peripheral mechanisms, including prolonged cell survival as attested by Bcl-2 levels. Conversely, a significant contraction of the CD31+ naive subset was observed in the absence of thymic activity. This was associated with impaired responses of purified naive CD4 T-cells to IL-7, namely, in vitro proliferation and upregulation of CD31 expression, which likely potentiated the decline in recent thymic emigrants. Additionally, we found no apparent constraint in the differentiation of naive cells into the memory compartment in individuals completely lacking thymic activity despite upregulation of DUSP6, a phosphatase associated with increased TCR threshold. Of note, thymectomized individuals featuring some degree of thymopoiesis were able to preserve the size and diversity of the naive CD4 compartment, further arguing against complete thymectomy in infancy. Overall, our data suggest that robust peripheral mechanisms ensure the homeostasis of CD31− naive CD4 pool and point to the requirement of continuous thymic activity to the maintenance of IL-7-driven homeostatic proliferation of CD31+ naive CD4 T-cells, which is essential to secure T-cell diversity throughout life.