Foscarnet-related Hypercalcemia During CMV Treatment in an Infant With SCID: A Case Report and Review of Literature.

Foscarnet is a main treatment for disseminated cytomegalovirus infection in immunocompromised patients. One of its documented side effects is hypocalcemia. Hypercalcemia, in contrast, was described anecdotally before, almost exclusively in adults with human immunodeficiency virus infection or posttransplantation. We describe a case of severe hypercalcemia during foscarnet treatment in an infant with IL-7 Rα deficient severe combined immunodeficiency, resolved after treatment cessation. We speculate that this unusual side effect is caused by foscarnet binding to the inorganic matrix of bone.

Interleukin-7 supports survival of T-cell receptor-ß-expressing CD4(-) CD8(-) double-negative thymocytes.

Among the milestones that occur during T-cell development in the thymus is the expression of T-cell receptor-ß (TCR-ß) and the formation of the pre-TCR complex. Signals emanating from the pre-TCR trigger survival, proliferation and differentiation of T-cell precursors. Although the pre-TCR is essential for these cell outcomes, other receptors, such as Notch and CXCR4, also contribute. Whether interleukin-7 (IL-7) participates in promoting the survival or proliferation of pre-TCR-expressing cells is controversial. We used in vitro and in vivo models of T-cell development to examine the function of IL-7 in TCR-ß-expressing thymocytes. Culturing TCR-ß-expressing CD4(-) CD8(-) double-negative thymocytes in an in vitro model of T-cell development revealed that IL-7 reduced the frequency of CD4(+) CD8(+) double-positive thymocytes at the time of harvest. The mechanism for this change in the percentage of double-positive cells was that IL-7 promoted the survival of thymocytes that had not yet differentiated. By preserving the double-negative population, IL-7 reduced the frequency of double-positive thymocytes. Interleukin-7 was not required for proliferation in the in vitro system. To follow this observation, we examined mice lacking CD127 (IL-7Rα). In addition to the known effect of CD127 deficiency on T-cell development before TCR-ß expression, CD127 deficiency also impaired the development of TCR-ß-expressing double-negative thymocytes. Specifically, we found that Bcl-2 expression and cell cycle progression were reduced in TCR-ß-expressing double-negative thymocytes in mice lacking CD127. We conclude that IL-7 continues to function after TCR-ß is expressed by promoting the survival of TCR-ß-expressing double-negative thymocytes.

Kinetics and activation requirements of contact-dependent immune suppression by human regulatory T cells.

Naturally occurring regulatory T cells (Tregs) maintain self tolerance by dominant suppression of potentially self-reactive T cells in peripheral tissues. However, the activation requirements, the temporal aspects of the suppressive activity, and mode of action of human Tregs are subjects of controversy. In this study, we show that Tregs display significant variability in the suppressive activity ex vivo as 54% of healthy blood donors examined had fully suppressive Tregs spontaneously, whereas in the remaining donors, anti-CD3/CD2/CD28 stimulation was required for Treg suppressive activity. Furthermore, anti-CD3/CD2/CD28 stimulation for 6 h and subsequent fixation in paraformaldehyde rendered the Tregs fully suppressive in all donors. The fixation-resistant suppressive activity of Tregs operated in a contact-dependent manner that was not dependent on APCs, but could be fully obliterated by trypsin treatment, indicating that a cell surface protein is directly involved. By add-back of active, fixed Tregs at different time points after activation of responding T cells, the responder cells were susceptible to Treg-mediated immune suppression up to 24 h after stimulation. This defines a time window in which effector T cells are susceptible to Treg-mediated immune suppression. Lastly, we examined the effect of a set of signaling inhibitors that perturb effector T cell activation and found that none of the examined inhibitors affected Treg activation, indicating pathway redundancy or that Treg activation proceeds by signaling mechanisms distinct from those of effector T cells.

Requirement of cognate CD4+ T-cell recognition for the regulation of allospecific CTL by human CD4+ CD127- CD25+ FOXP3+ cells generated in MLR.

Although immunoregulation of alloreactive human CTLs has been described, the direct influence of CD4(+) Tregs on CD8(+) cytotoxicity and the interactive mechanisms have not been well clarified. Therefore, human CD4(+)CD127(-)CD25(+)FOXP3(+) Tregs were generated in MLR, immunoselected and their allospecific regulatory functions and associated mechanisms were then tested using modified (51)Chromium release assays (Micro-CML), MLRs and CFSE-based multi-fluorochrome flow cytometry proliferation assays. It was observed that increased numbers of CD4(+)CD127(-)CD25(+)FOXP3(+) cells were generated after a 7 day MLR. After immunoselection for CD4(+)CD127(-)CD25(+) cells, they were designated as MLR-Tregs. When added as third component modulators, MLR-Tregs inhibited the alloreactive proliferation of autologous PBMC in a concentration dependent manner. The inhibition was quasi-antigen specific, in that the inhibition was non-specific at higher MLR-Treg modulator doses, but non-specificity disappeared with lower numbers at which specific inhibition was still significant. When tested in micro-CML assays CTL inhibition occurred with PBMC and purified CD8(+) responders. However, antigen specificity of CTL inhibition was observed only with unpurified PBMC responders and not with purified CD8(+) responders or even with CD8(+) responders plus Non-T "APC". However, allospecificity of CTL regulation was restored when autologous purified CD4(+) T cells were added to the CD8(+) responders. Proliferation of CD8(+) cells was suppressed by MLR-Tregs in the presence or absence of IL-2. Inhibition by MLR-Tregs was mediated through down-regulation of intracellular perforin, granzyme B and membrane-bound CD25 molecules on the responding CD8(+) cells. Therefore, it was concluded that human CD4(+)CD127(-)CD25(+)FOXP3(+) MLR-Tregs down-regulate alloreactive cytotoxic responses. Regulatory allospecificity, however, requires the presence of cognate responding CD4(+) T cells. CD8(+) CTL regulatory mechanisms include impaired proliferation, reduced expression of cytolytic molecules and CD25(+) activation epitopes.

Loss of CD127 & increased immunosenescence of T cell subsets in HIV infected individuals.

BACKGROUND & OBJECTIVES: HIV infection is characterized by a perturbation in T cell homeostasis, leading to alteration in T cell subsets. In addition to alteration in differentiation, HIV infection also leads to change in T cell survival and regenerative capacity, as suggested by differential expression of CD127 and CD57. We evaluated the expression patterns of CD127 and CD57 on CD4 and CD8 effector, memory and naïve T cell subsets in HIV-infected and uninfected individuals. METHODS: We characterized T cell subsets based on expression of these markers, and compared their expression pattern in HIV infected subjects and uninfected controls. We further assessed therapy generated changes in these subsets and expression of CD127 and CD57 on them. RESULTS: There was a generalized decrease in naïve CD4 and CD8 T cells in HIV infected subjects. These changes in T cell subset distribution were related to antigen load. CD127 expression was significantly reduced in T cells from HIV infected subject. In association to this, HIV infected subjects had higher percentage of T cell subsets expressing CD57. Increased CD57 and reduced CD127 expression correlated with plasma viraemia and CD8 T cell activation state. Incomplete restoration of T cell subset proportions was observed, despite suppression of viral replication and increase in CD4 T cell counts. Further, the improvement was more pronounced in CD127 expression. INTERPRETATION & CONCLUSIONS: HIV infected subjects have reduced T cell regenerative capacity along with increased senescence, highlighting decreased proliferation and effector activities.

Delayed onset of (severe) combined immunodeficiency (S)CID (T-B+NK+): complete IL-7 receptor deficiency in a 22 months old girl.

BACKGROUND: Usually IL-7 receptor deficiency presents as (T-B+NK+) (Severe) Combined Immunodeficiency (SCID) within the first six months of life. All published IL-7R-deficient patients so far have been diagnosed and received stem cell transplantation within the first year of life. PATIENT AND METHODS: We present a female patient born to non-consanguineous German parents with delayed manifestation. She presented with superinfected dermatitis at 6 months of life and developed a first pneumonia at age 9 months. On admission to our department at 22 months the patient presented with severe T cell lymphopenia. PNEUMOCYSTIS JIROVECI pneumonia was diagnosed from broncho-alveolar lavage fluid. RESULTS: Sequencing of IL7RA in the patient revealed compound heterozygous mutations. FACS analysis showed no expression of IL-7 receptor alpha-chain on the patient's lympho- and monocytes. The patient successfully received haematopoietic stem cell transplantation from a 9/10 matched unrelated donor at age 24 months. CONCLUSION: [corrected] Despite almost absent T cell functions clinical symptoms occurred late compared to previously published patients. Thus even in patients with moderate clinical symptoms and delayed onset a (T-B+NK+) (Severe) Combined Immunodeficiency ((S)CID)) due to missing IL-7 receptor signalling must be considered.