Impact of Pneumocystis jirovecii pneumonia on kidney transplant outcome

Backgrounds

Pneumocystis jirovecii pneumonia (PCP) remains an important cause of morbidity and mortality in kidney transplant recipients. While the acute phase toxicity in patients with PCP is well-characterized, there is a lack of data on the effects of PCP on long-term graft outcome.

Method

This retrospective observational study analyzed 1502 adult patients who underwent kidney transplantation at Seoul National University Hospital between 2000 and 2017. After a propensity score matching was performed, the graft and survival outcomes were compared between PCP-negative and PCP-positive groups.

Results

A total of 68 patients (4.5%) developed PCP after transplantation. The multivariable Cox analysis showed that positivity for cytomegalovirus and lack of initial oral antibiotic prophylaxis were risk factors of post-transplant PCP. The PCP-positive group had higher hazard ratios of graft failure [adjusted hazard ratio (HR), 3.1 (1.14–8.26); P = 0.027] and mortality [adjusted HR, 11.0 (3.68–32.80); P < 0.001] than the PCP-negative group. However, the PCP event was not related with subsequent development of de novo donor-specific antibodies or pathologic findings, such as T-cell or antibody mediated rejection and interstitial fibrosis and tubular atrophy.

Conclusions

PCP is a risk factor of long-term graft failure and mortality, irrespective of rejection. Accordingly, appropriate prophylaxis and treatment is needed to avoid adverse transplant outcomes of PCP.

Electronic supplementary material

The online version of this article (10.1186/s12882-019-1407-x) contains supplementary material, which is available to authorized users.

Development of transplant immunosuppressive agents - considerations in the use of animal models

INTRODUCTION

The development of all immunosuppressant agents to date has involved the experimental use of large and small animal models. Over the last half-century, immunosuppressive drugs have extended the lives of transplant patients worldwide. However, the use of animal models in the development of these drugs is not perfect, and this has brought to light a number of issues including idiosyncratic reactions that are found in animal models but not in humans. The 2006 highly publicized case of the 'elephant man' TGN 1412 drug trial highlights the importance of being cogent of the limitations of animal models. Areas covered: This review covers the utility and limitations of the use of animal models for the development of immunosuppressant agents. This includes both large and small animal models, particularly rodent models in the transplant setting. Expert opinion: The use of animal models represents a critical stage in the development of immunosuppressive drugs. Limitations include physiological differences to humans; this is especially true of immunologically naïve lab rodents with small memory cell populations. Toxic drug levels may differ widely between species. Animal models are also costly and raise ethical concerns. However, there is currently no way to recreate the complex environment of the human immune system purely in vitro.

Spontaneous restoration of transplantation tolerance after acute rejection

Transplantation is a cure for end-stage organ failure but, in the absence of pharmacological immunosuppression, allogeneic organs are acutely rejected. Such rejection invariably results in allosensitization and accelerated rejection of secondary donor-matched grafts. Transplantation tolerance can be induced in animals and a subset of humans, and enables long-term acceptance of allografts without maintenance immunosuppression. However, graft rejection can occur long after a state of transplantation tolerance has been acquired. When such an allograft is rejected, it has been assumed that the same rules of allosensitization apply as to non-tolerant hosts and that immunological tolerance is permanently lost. Using a mouse model of cardiac transplantation, we show that when Listeria monocytogenes infection precipitates acute rejection, thus abrogating transplantation tolerance, the donor-specific tolerant state re-emerges, allowing spontaneous acceptance of a donor-matched second transplant. These data demonstrate a setting in which the memory of allograft tolerance dominates over the memory of transplant rejection.

Transplantation tolerance and its outcome during infections and inflammation

Much progress has been made toward understanding the mechanistic basis of transplantation tolerance in experimental models, which implicates clonal deletion of alloreactive T and B cells, induction of cell-intrinsic hyporesponsiveness, and dominant regulatory cells mediating infectious tolerance and linked suppression. Despite encouraging success in the laboratory, achieving tolerance in the clinic remains challenging, although the basis for these challenges is beginning to be understood. Heterologous memory alloreactive T cells generated by infections prior to transplantation have been shown to be a critical barrier to tolerance induction. Furthermore, infections at the time of transplantation and tolerance induction provide a pro-inflammatory milieu that alters the stability and function of regulatory T cells as well as the activation requirements and differentiation of effector T cells. Thus, infections can result in enhanced alloreactivity, resistance to tolerance induction, and destabilization of the established tolerance state. We speculate that these experimental findings have relevance to the clinic, where infections have been associated with allograft rejection and may be a causal event precipitating the loss of grafts after long periods of stable operational tolerance. Understanding the mechanisms by which infections prevent and destabilize tolerance can lead to therapies that promote stable life-long tolerance in transplant recipients.

Infection among adult small bowel and multivisceral transplant recipients in the 30-day postoperative period

BACKGROUND

Intestinal transplantation is a potential option for patients with short gut syndrome (SGS), and infection is common in the postoperative period. The aim of our study was to identify the incidence and characteristics of bacterial and fungal infections of adult small bowel or multivisceral (SB/MV) transplantation recipients in the 30-day postoperative period.

METHODS

This retrospective chart review assessed the incidence and characteristics of bacterial and fungal infections in patients who underwent SB/MV transplant at our center between April 2004 and November 2008. Patient data were retrieved from computerized databases, flow-charts, and medical records.

RESULTS

A total of 40 adult patients with a mean age of 38.7 ± 13.4 years received transplants during this period: 27 patients received isolated SB, 12 received MV, and 1 received SB and kidney. Our immunosuppressive regimen included basiliximab for induction, and tacrolimus, sirolimus, and methylprednisolone for maintenance therapy. The most common indications for transplant were SGS, intestinal ischemia, Crohn's disease, trauma, motility disorders, and Gardner's syndrome. We report a 30-day postoperative infection rate of 57.5% and mean time to first infection of 10.78 ± 8.99 days. A total of 36 infections were documented in 23 patients. Of patients who developed infections, 56.5% developed 1 infection, 30.4% developed 2 infections, and 13% developed 3 infections. The most common site of infection was the abdomen, followed by blood, urine, lung, and wound infection. The isolates were gram-negative bacteria in 49.3%, gram-positive bacteria in 39.4%, and 11.3% were fungi. The most common organisms were Pseudomonas (19%), Enterococcus (15%), and Escherichia coli (13%). Overall, 47% of infections were due to drug-resistant pathogens; 31% of E. coli and Klebsiella species were extended-spectrum beta-lactamase-producing organisms, 36% of Pseudomonas was multidrug resistant (MDR), 75% of Enterococcus was vancomycin resistant, and 100% of Staphylococcus aureus was methicillin resistant.

CONCLUSION

These findings demonstrate that bacterial and fungal infections remain an important complication in SB/MV transplant recipients within the early postoperative period. Infections due to MDR organisms have emerged as an important clinical problem in this patient population.

Toll-like receptor signaling in transplantation

PURPOSE OF REVIEW

This review summarizes recent advances in the role of endogenous and exogenous Toll-like receptor ligands in the activation and inhibition of immune responses in transplantation.

RECENT FINDINGS

During an alloresponse, Toll-like receptors can be engaged by both damage-induced endogenous ligands or microbial-associated molecular patterns. The damage-induced molecule high mobility group box 1 protein and its binding to Toll-like receptor 4 have been identified as major initiators of antitumor and antitransplant immune responses. Type I interferon signaling plays an important role in the pro-rejection effect mediated by Toll-like receptor agonists and some bacteria. Similar pathways, however, in neonates can result in inhibition rather than activation of alloimmune responses.

SUMMARY

The consequences of Toll-like receptor engagement by endogenous and exogenous ligands in transplantation may depend on the relative induction of inflammatory and regulatory pathways and the stage of development of the immune system.

The impact of infection and tissue damage in solid-organ transplantation

Investigations over the past two decades are revealing complexities in the regulation of the innate immune response, and how this response, in turn, controls adaptive immunity. Microbial exposure, infections and tissue damage that accompany solid-organ transplantation result in the release of pathogen- and damage-associated molecular patterns, as well as pathogen- or allograft-derived antigens. Here, we review these triggers of innate and adaptive immunity, and discuss emerging paradigms of the many ways in which infections and tissue damage might directly or indirectly affect alloreactivity and the outcome of transplanted allografts.

IL-6 induced by Staphylococcus aureus infection prevents the induction of skin allograft acceptance in mice

Clinical correlations between bacterial infections and rejection suggest a hypothesis that innate immune stimulation by bacterial infections results in the production of inflammatory cytokine that facilitate bystander T-cell activation, increased alloreactivity and inhibition of tolerance induction. Previous studies demonstrated that IFNβ produced during an infection with a model bacterium, Listeria monocytogenes, prevented the induction of transplantation tolerance in mice with anti-CD154 and donor-specific transfusion (DST) (1). We investigated the impact of two clinically relevant bacterial infections at the time of transplantation on the ability of anti-CD154 and DST to induce skin allograft acceptance in mice. Staphylococcus aureus (SA) infection prevented skin allograft acceptance whereas maximally tolerated doses of Pseudomonas aeruginosa infection had no effect. SA induced an acute production of IL-6, which was necessary and sufficient for the prevention of skin allograft acceptance. Furthermore, a single pulse of methylprednisolone modulated IL-6 production during SA infection and facilitated skin allograft acceptance in SA-infected recipients. Taken together, our results suggest that bacterial infections elicit specific proinflammatory cytokines signatures that can serve as barriers to tolerance induction, and that inhibiting the production of or neutralizing these inflammatory cytokines can synergize with costimulatory blockade-based therapies to facilitate the development of transplantation tolerance.

Bacterial infections, alloimmunity, and transplantation tolerance

Transplantation of solid organs across histocompatibility barriers in the absence of immunosuppression is invariably followed by acute allograft rejection. Although several immunosuppressive regimens have been developed to prevent allograft rejection, these global immunosuppressive agents effectively inhibit all T cells, leaving the host vulnerable to infections. Thus, a major goal in transplantation immunology is to induce donor-specific tolerance that results in the extended suppression of allograft-specific immune responses, while leaving the remainder of the immune system competent to fight infections and malignancies. Initial successes in identifying approaches that successfully induce transplantation tolerance in experimental models have led to a newer research focus of identifying potential barriers to the induction of such tolerance as well as events that may reverse established allograft tolerance. Both clinical and experimental studies have identified bacterial infections as a possible trigger of allograft rejection. Recently, experimental models of transplantation tolerance have identified that bacterial signals can promote acute allograft rejection either by preventing the induction of transplantation tolerance or by reversing tolerance after it has been stably established. This review summarizes experimental and clinical literature supporting the hypothesis that bacterial infections and innate immunity can qualitatively and quantitatively alter adaptive alloreactivity through effects on innate immune responses.

Antagonistic effect of toll-like receptor signaling and bacterial infections on transplantation tolerance

The induction of donor-specific tolerance remains a major goal in the field of transplantation immunology. Therapies that target costimulatory molecules can induce tolerance to heart and pancreatic islet allografts in mouse models, but fail to do so after transplantation of skin or intestinal allografts. We have proposed that organs colonized by commensal bacteria such as skin, lung, and intestine may be resistant to such therapies as a result of bacterial translocation at the time of transplantation, which may promote antigen-presenting cell maturation and the production of proinflammatory cytokines, consequently enhancing responses of alloreactive T cells. Our results indicate that the inability to sense signaling by most toll-like receptors (TLRs), as well as by interleukin-1R and -18R, as a result of genetic ablation of myeloid differentiation factor 88 promotes the acceptance of skin allografts. Conversely, TLR signals and infections by a model bacterium, Listeria monocytogenes (LM), at the time of transplantation can prevent the induction of transplantation tolerance. The effects of the TLR9 agonist CpG are myeloid differentiation factor 88-dependent, whereas the prorejection capacity of LM depends on the intracellular sensing of LM and the production of type I interferon. Therefore, transiently targeting these innate, proinflammatory pathways may have therapeutic value to promote transplantation tolerance.