Late-Onset Hemophagocytic Lymphohistiocytosis in a Lung Transplant Patient: A Case of T-Cell Post-Transplant Lymphoproliferative Disorder

Introduction

Hemophagocytic lymphohistiocytosis (HLH) is a rare and life-threatening hyper-inflammatory syndrome characterized by the uncontrolled activation of the immune system. It features severe cytopenia resulting from uncontrolled hemophagocytosis, as well as clinical and biological signs associated with the cytokine storm [1,2]. It is artificially divided into “primary HLH” (or familial HLH) when resulting from a biallelic genetic defect impairing the function of natural killer or cytotoxic T lymphocytes and “secondary HLH” when referring to sporadic cases that can be triggered by infections, malignancies, autoimmune disorders, or metabolic disorders in patients with a predisposing condition, such as immunodeficiency [3].

HLH pathophysiology relates to impaired cytotoxic function of natural killer cells and cytotoxic T lymphocytes, ultimately leading to uncontrolled activation of macrophages and histiocytes, resulting in systemic inflammation. HLH therefore presents with varied symptoms including fever, hepatosplenomegaly, cytopenias, hyperferritinemia, hypertriglyceridemia, and coagulopathy. Most genetic alterations recognized to be responsible for familial HLH are thus directly affecting proteins involved in cytotoxicity, such as perforin, Munc13-4, Syntaxin 11, Munc18-2, or Rab27A, although other mutations in genes linked with inflammasome dysregulation have also been described [4].

Since the identification of monoallelic mutations in sporadic HLH cases, the distinction between primary and secondary HLH has been challenged, with HLH now considered a “continuum of inflammatory conditions, where the risk of developing the syndrome is the result of the subtle balance between a pre-disposed genotype and environmental factors” [4]. However, the pathophysiology of secondary HLH has not yet been fully elucidated and likely involves multiple factors, including monoallelic mutations, whose ability to induce impaired cytotoxicity remains to be demonstrated, sustained toll-like receptor activation by infectious or autoimmune triggers, and host immune status [2].

The diagnosis of HLH is challenging due to its nonspecific clinical manifestations, and the H-score [5], derived from various clinical and laboratory parameters, helps to assess its probability based on the presence of clinical and biological findings. However, HLH diagnosis often requires a comprehensive evaluation, including bone marrow biopsy/aspiration, revealing hemophagocytosis, molecular tests, and imaging studies to detect organ involvement [1].

HLH management usually aims at controlling cytokine storm and preventing organ damage and involves immunosuppression with corticosteroids and etoposide to suppress immune activation, while intravenous immunoglobulin therapy can modulate the immune response, and rituximab can be used when a B-cell malignancy is associated. Hematopoietic stem cell transplantation remains the curative option for primary HLH or refractory cases [6]. The prognosis of HLH depends on the underlying cause, early diagnosis, and the rapidity of treatment initiation. Mortality rates are high if untreated or in cases of delayed recognition. In secondary HLH, addressing the triggering factor is crucial for successful management. Complications such multi-organ failure, bleeding disorders, and neurological impairment contribute to the overall morbidity and mortality.

Case Report

We present the case of a 67-year-old female lung transplant recipient who presented at the Emergency Department with fever, chills, and asthenia. She underwent sequential bilateral lung transplantation (LT) 11 years earlier for chronic obstructive pulmonary disease Gold stage IV/E. Aside from this condition, her medical history prior to transplantation included an appendectomy, osteoporosis treated with bisphosphonates, and dyslipidemia. The early period after LT was characterized by an acute cellular rejection (A2Bx) after 1 month, which was treated with corticosteroids, and by the development of bilateral bronchial suture stenosis that required Argon treatment on the left side. Additionally, she had a Pseudomonas aeruginosa pneumonia in 2016, underwent an episode of left eye uveitis due to Toxoplasma gondii in 2020, which was successfully treated with TMP/SMX, and had a SARS-CoV2 infection without lung involvement in May 2022. She also displayed KDIGO stage G4 chronic kidney disease due to calcineurin inhibitor nephrotoxicity, with an estimated glomerular filtration rate of 26 mL/min/1.73 m2.

She experienced a decrease in forced expiratory volume in the first second (FEV1) after 8 years, suggestive of obstructive chronic allograft dysfunction (CLAD/BOS). However, the FEV1 remained stable during the next 3 years. Her latest pulmonary function tests showed a FEV1 of 1770 mL (80% of the predicted values and 69% of post-transplant baseline FEV1), with a FEV1/FVC ratio of 0.66.

She presented at the Emergency Department with asthenia and fever at home accompanied by chills. The clinical examination on day 1 was normal except for a slow skin pinch test. Vital signs measurements revealed a marked fever of 39°C, mild tachycardia at 93 beats per min, grade I arterial hypertension at 155/90 mm Hg, and normal resting pulse oxygen saturation at 97% at room air. Her Glasgow coma scale score was measured at 15/15. A chest X-ray was normal. Subsequent blood tests (Table 1) mainly indicated pancytopenia, with WHO grade II anemia, grade II thrombocytopenia, and grade III leucopenia. Additionally, a mild elevation of C-reactive protein was noted, along with increased ferritin and triglycerides levels, and grade I acute kidney injury with associated hypobicarbonatemia. Tacrolemia was within the required therapeutic range. Bacteriological samples were collected, including blood culture, urinary culture, and a nasal swab for SARS-CoV2, influenza A and B, and respiratory syncytial virus, all of which returned negative results.

Further tests were performed to investigate the etiology of pancytopenia. Levels of B12 vitamin and folate were normal. Serological tests for hepatitis A virus, hepatitis B virus, hepatitis C virus, HIV, and parvovirus B19 were negative. While Epstein-Barr virus (EBV) IgG tested positive, IgM was negative. Serum complement levels and protein electrophoresis were normal. Cytomegalovirus, parvovirus B19, EBV, and HHV6 PCR tests all returned negative. Antinuclear antibodies, rheumatoid factor and antineutrophilic cytoplasmic antibody were negative.

Prophylactic SMX-TMP was discontinued because of its potential myelotoxicity, and the patient was admitted to the hospital for further investigation. On day 2, bone marrow aspiration and biopsy were performed. Flow cytometry analysis on bone marrow aspirates showed the presence of 2.4% CD34+ cells among the CD45+ cells. These cells also expressed CD117, CD33, and HLA-DR and were immunophenotypically compatible with myeloblasts. Bone marrow aspirates revealed a 46, XX karyotype as well as medullary hypoplasia, without abnormal cell populations or dysplasia, thereby excluding acute myeloid leukemia, myelodysplastic syndrome, or solid neoplasia infiltration. In addition, rare hemophagocytosis images were observed (Figure 1). At this point, the calculated H-score was 120, indicating a 5% to 9% probability of HLH [5] (Table 2).

On day 2, corticosteroids were initiated at a dosage of 1 mg/kg and mycophenolate mofetil was discontinued. The patient continued to experience high fever (39.5°C), and increased triglycerides and ferritin. A total body computed tomography scan was performed, mainly showing splenomegaly with a spleen length of 18 cm. On day 5, the H-Score was 207, indicating an 88% to 93% probability of HLH. Consequently, a provisional diagnosis of HLH was established, leading to the initiation of a treatment with etoposide (dose reduced to 100 mg due to chronic kidney disease) and dexamethasone (5 mg twice daily). Over the subsequent 12 days, the patient exhibited gradual improvement: no new episodes of fever occurred, and ferritin levels seemed to stabilize, while triglyceride levels decreased. However, the hemogram did not show improvement, with persisting grade IV anemia, leucopenia, and thrombopenia, with iterative platelets and red blood cells transfusion being required.

In the meanwhile, rare causes of HLH, in particular infection-induced HLH, were investigated. Serological tests for Toxoplasma, Coxiella burnetii, Toxocara canis, Brucella, Leptospira, Echinococcus granulosus and multilocularis, Mycoplasma pneumoniae, Treponema pallidum, Borrelia burgdorferi, and Trichinella spiralis all returned negative. Serum galactomannan was negative on 2 separate occasions (on days 11 and 21). Remarkably, very high serum levels of soluble CD25 were observed (146 973 pg/mL, reference values <2000 pg/mL), further supporting the diagnosis of HLH. A positron emission tomography scan conducted on day 17 revealed multiple hyper-metabolic lymph nodes in the chest and abdomen, along with hypermetabolic splenomegaly, suggestive of ongoing diffuse lymphoproliferative disease. The most hypermetabolic lymph node, located in station 4R, exhibited a standardized uptake value of 19.8. Due to the lesion’s limited size (5 mm) and persistent thrombopenia (<10 000/µL, despite multiple platelet transfusion), an endobronchial ultrasound-guided transbronchial needle biopsy was not performed.

On day 19, the patient experienced recurrence of fever (38.2°C) without apparent clinical signs of infection. Empirical treatment with intravenous piperacilline-tazobactam was initiated, and etoposide was recommenced (100 mg twice a week), while dexamethasone dosage was increased (5 mg 3 times daily). However, no noticeable improvement was observed in the next couple of days, and intravenous immunoglobulins (20 g/d) were incorporated to the treatment regimen on day 22. On the same day, vancomycin-sensitive Enterococcus faecium colonies were detected in the blood cultures, prompting the initiation of vancomycin therapy. Due to the presence of bacteriemia coupled with pancytopenia, the patient was transferred to the Intensive Care Unit on day 23 for close monitoring. On day 25, complementary results of a cytogenetic analysis of the bone marrow aspirates revealed the presence of a pseudodiploid clone highly suggestive of underlying neoplastic condition. Rituximab (375 mg/m2) was initiated as a salvage therapy for a suspected B-cell post-transplant lymphoproliferative disorder.

Unfortunately, the patient’s clinical condition rapidly deteriorated, with increased oxygen requirements, metabolic acidosis, and acute kidney injury. Despite vancomycin reaching therapeutic serum levels, blood cultures continued to show the presence of Enterococcus faecium. In accordance with the patient’s wishes, we did not proceed with orotracheal intubation, and a decision was made to initiate a therapeutic de-escalation, and the patient died on day 28.

With the patient’s family consent, an autopsy was performed, revealing lymphoid infiltration in the mediastinal lymph nodes, liver, and bone marrow, alongside signs of splenic hematopoiesis. While some lymphocytes expressed CD3 (Figure 2), CD20 staining did not provide significant contributions. These results were concordant with the final bone marrow aspirates results, which revealed the presence of a minor pseudodiploid and complex clone (46,XX,del(6)(q14q26),i(8)(q10),-10,idic(21) (q10),+mar1,+mar2), suggestive of underlying neoplasia. The T-cell receptor analysis by PCR revealed a monoclonal pattern (loci rearrangements of TCR gamma and TCR beta, but polyclonal for Ig heavy chain and Ig kappa), witnessing a monoclonal T-cell proliferation. According to WHO 2022 diagnosis criteria, a diagnosis of Ann-Arbor stage IV, non-EBV-mediated, monomorphic T-cell post-transplant lymphoproliferative (PTLD) was established.

Discussion

The present manuscript reports a thus far unreported case of secondary PLTD-related HLH occurring exceptionally late (11 years) after LT. Despite timely adapted treatment and transient stabilization of her clinical and biological state, our patient developed a refractory septic condition that unfortunately led to her death.

Although secondary HLH is a rare condition among solid organ transplant (SOT) recipients (estimated prevalence approximately 1 in 3000), several case reports and case series have documented its occurrence within this specific population [7,8]. Whether immunosuppression itself may favor HLH or whether the increased incidence of HLH among SOT recipients, compared with the general population (prevalence 1 in 800 000), is due to increased susceptibility to infections and/or neoplasia is not elucidated [9,10]. Recently, a thorough review identified 179 cases of HLH following SOT, published between 1979 and 2023 [11]. Reported death rates are dismal, ranging from 50% in kidney and liver transplant recipients to 90% in recipients of other organs (mostly lung and heart), suggesting that heavier immunosuppression regimens might be a poor prognostic factor. Infections accounted for the most frequent trigger (82%), far above neoplasms (8%) and other rarer causes. In LT recipients specifically, only 8 cases of secondary HLH have been reported between 2010 and 2022 [12–17]. All occurred during the first year after transplant (median: 3 months after LT), and all but one led to death. Four were reported to be due to infection, while no cause was identified for the others.

Strikingly, in the present case, the patient simultaneously presented with 2 rare T-cell-related conditions. PTLD is a rare but well-recognized complication following SOT, with a reported incidence between 1% and 5% [4,18–22]. In 85% of cases, it occurs as an EBV-driven B-cell PTLD. Whether T-cell, versus B-cell, lymphoma is more likely to induce HLH is not known. In a recent article reviewing lymphoma-associated HLH, T-cell and B-cell non-Hodgkin lymphoma each accounted for 45% of the cases, with poorer survival observed in T-cell lymphoma-related HLH [23].

The management of HLH in solid organ transplant recipients is challenging, as immunosuppression is thought to be able to favor HLH [11]. In our patient, the immunosuppression regimen was lightened, with reduced tacrolimus serum objectives and discontinuation of mycophenolate mofetil. However, no consensus currently exists regarding the management of immunosuppressive regimens in the course of HLH treatment, although most case reports describe discontinuation of calcineurin inhibitors.

Conclusions

Secondary HLH is a rare and life-threatening condition in SOT recipients, with an even poorer prognosis among LT recipients. It is more likely to occur early after transplantation, but we report a case in an 11-year LT recipient. The respective contributions of immunosuppression and neoplasia, whose frequency increases in immunocompromised individuals, remain unclear. Although HLH is most often due to infections, neoplasia-related HLH does indeed occur, and underlying neoplasms should be sought in at-risk patients. Adjustment of the immunosuppression regimen is often suggested, but clearer guidelines are required in the field to improve its poor outcomes.