Passenger lymphocyte syndrome after living-donor kidney transplantation with minor ABO incompatibility: a case report

INTRODUCTION

The passenger lymphocyte syndrome (PLS) is a graft-versus-host disease reaction that may occur early after hematopoietic stem cell transplantation (HSCT) or solid organ transplantation, particularly renal transplantation^1,2. It arises in cases of minor ABO incompatibility between donor and recipient^3,4. PLS results in immune-mediated hemolysis of the recipient’s red blood cells due to viable donor-derived lymphocytes persisting within the graft and producing ABO isohemagglutinins directed against the recipient’s incompatible ABO erythrocyte antigens^5–8.

The onset of PLS typically occurs within 1–3 weeks after the transplant and the syndrome is usually self-limiting^9,10. Anti-ABO antibodies gradually decrease until they disappear in approximately 3 months because of the short lifespan of donor B lymphocytes. As ABO antigens are expressed on various cell types, not only erythrocytes, the donor antibodies are progressively neutralized^1,6,8. We report the case of a 28-year-old woman who underwent a living-donor kidney transplant. The recipient’s blood group was A RhD-positive, and the father donor’s group was O RhD-positive.

CASE PRESENTATION AND RESULTS

A 28-year-old woman of mixed ethnicity (maternal Caucasian, paternal North African) with a history of Kawasaki arteritis and glomerulonephritis, developed progressive renal failure, requiring dialysis for 4 months, and underwent living-donor kidney transplantation^2,3. The patient’s blood group was registered in our database as type A1. Post-transplant immunosuppression included high-dose corticosteroids, basiliximab, tacrolimus, and mycophenolate mofetil. She also continued treatment with carvedilol, omeprazole, epoetin alfa, prophylactic enoxaparin, and cotrimoxazole. Upon discharge, her hemoglobin level was 112 g/L (Table I, Figure 1), platelet count was normal, and neutrophilic leukocytosis was attributed to steroids. On day 18 after transplantation, she presented to the emergency department complaining of right shoulder and scapular pain persisting for several days. Laboratory investigations revealed severe anemia (hemoglobin 49 g/L), a normal platelet count, a white blood cell count of 22.6×10³/μL, elevated reticulocytes, preserved renal function, normal coagulation parameters, negative inflammatory indices, and evidence of hemolysis: total bilirubin 2.6 mg/dL (direct 0.9 mg/dL), lactate dehydrogenase 561 U/L, and undetectable haptoglobin (Table I, Figure 1). Computed tomography angiography excluded bleeding but revealed subocclusive thrombosis of the right internal jugular and brachiocephalic veins (previous catheter site). One unit of A RhD-positive red blood cells was assigned and transfused after verification of the ABO blood group and a negative TCI result with Type & Screen, and she was admitted to the Nephrology Unit with suspected post-transplant hemolytic anemia^6,9. The hematologists excluded paroxysmal nocturnal hemoglobinuria, glucose-6- phosphate dehydrogenase deficiency, and hemolytic uremic syndrome. The patient reported fatigue, headache and emission of dark-colored urine, some days before hospitalization. She had no lymphadenopathy or hepatosplenomegaly at physical examination. Peripheral blood smear showed marked anisopoikilocytosis, microspherocytes, and a few schistocytes. Criteria for microangiopathic syndrome were not met (low PLASMIC score). The findings were consistent with hemolytic anemia^6,9. Anticoagulant therapy was initiated for the venous thromboses. Immunohematological testing showed a negative indirect Coombs’ test (IAT) with O-type panel cells but strongly positive for A1 and A2 type cells with A1-A2-B-O-type panel cells. A direct antiglobulin test (DAT) for IgG and C3d was strongly positive. Elution studies demonstrated the presence of anti-A antibodies bound to the patient’s red blood cells^5,7. These findings strongly supported the diagnosis of PLS, where donor-derived lymphocytes (group O) within the graft produce anti-A antibodies against the recipient’s erythrocytes (group A)^2–6. The patient was subsequently managed jointly with the Transfusion Medicine Service. The severe clinical presentation occurring a few days after transplantation, the evidence of immune-mediated active hemolysis, the need to remove from circulation both the free hemoglobin derived from hemolysis and the donor’s anti-A antibodies, together with data reported in the literature, led to the identification of plasma exchange (PEX) as a possible initial therapeutic approach. Urgent PEX was performed, exchanging 1.2 plasma volumes (3,500 mL of saline solution with 5% albumin). The procedure was well tolerated and vital parameters remained stable throughout. It was recommended that any further blood transfusions be restricted to group O –the donor’s blood group–to prevent further hemolysis, and this information was recorded in the transfusion service database. The need for additional PEX was to be reassessed according to trends in hemolytic markers. At the beginning of the procedure discarded plasma and plasma within the PEX circuit showed mild visible hemolysis; otherwise laboratory testing performed in discarded plasma at the end of the procedure confirmed normal free hemoglobin levels (due to dilution in the waste plasma). So, active hemolysis had largely subsided by the time of admission⁵. In the following days, immunosuppressive therapy was intensified with intravenous methylprednisolone boluses (500 mg/day for 4 consecutive days), followed by oral prednisone (16 mg/day). Due to significant anemia, four additional units of irradiated group O Rh-positive red blood cells were transfused after pre trasfusional tests including serological cross-matching. Irradiation was performed to inactivate residual viable lymphocytes and prevent immune reactions in an already immunocompromised recipient^5,7. Anticoagulation was continued (enoxaparin, then edoxaban 30 mg/day for 3 months). Hemoglobin levels progressively stabilized, hemolysis indices decreased, and renal function remained normal (creatinine −1.0 mg/dL). The patient was discharged on day 27 after transplantation with the diagnosis of hemolytic anemia secondary to PLS and jugular-brachiocephalic vein thrombosis. Follow-up immunohematological tests after a month showed negative IAT and DAT, and anti-A antibody titers (IgG and IgM) of 1:1, consistent with resolution of the syndrome. Regarding renal transplantation, isohemoagglutinin titration is routinely performed only in cases of major or bidirectional ABO incompatibility. In this case, classified as a minor incompatibility, the donor was tested for ABO/RhD group, Rh and Kell phenotype, and for TCI (as recommended in ABO antibody titrations), which was negative but donor antibody titration was not undertaken. Post hoc testing of the donor’s serum revealed anti-A titers within normal limits (IgG 32; IgM 16), excluding a so-called “dangerous O” donor. Similarly, the recipient’s post-transplant anti-A titers were low (IgG 16; IgM 8), consistent with immunosuppression and also that anti-A antibodies were bound to the recipient’s A antigens on red blood cells, endothelium and tissues rather than circulating freely.

Table I.

Temporal trends of the hemato-chemical and immunohematological parameters assessed in our patient after renal transplantation

Parameters	d 13 post- transpl	d 17 post- transpl	d 18 post- transpl	d 19 post- transpl	d 20 post- transpl	d 21 post- transpl	d 27 post- transpl	d 55 post- transpl	d 88 post- transpl
		Admission	PEX				Discharge
WBC (×10 9 /L)	22.7	22.6	22.3	17.5	23.7	20.0	10.1	12.9	7.3
RBC (×10 12 /L)	3.29	1.33	1.48	3.16	2.60	3.04	3.23	3.61	4.54
Hb (g/L)	112	49	53	97	80	92	100	110	137
Hct (L/L)	0.32	0.14	0.15	0.29	0.23	0.27	0.31	0.34	0.43
MCV (fL)	97	103	98	97	80	88.8	96.3	94.5	95.6
PLT (×10 9 /L)	285	362	353	304	298	288	314	343	294
BUN (mg/dL)	26	38	38	22	31	31	25	25	23
Creatinine (mg/dL)	1.3	1.11	1.09	0.88	1.04	0.95	1.00	1.03	1.12
GFR (estimated)	56	68	69	90	73	82	77	74	67
Total bilirubin (mg/dL)	-	2.6	2.9	3.0	1.5	1.1	-	0.7	0.4
Direct bilirubin (mg/dL)	-	0.9	0.9	0.4	0.6	0.5	-	0.3	0.2
LDH (U/L) [ref <210]	-	561	-	-	267	253	-	277	-
Haptoglobin	-	-	< 0.10	-	< 0.10	< 0.10	-	0.2	-
IAT	-	Neg	Neg	-	Neg	Neg	-	Neg	-
DAT	-	-	Pos	-	Pos	Pos	-	Weak	-
Monospecific DAT	-	-	Pos IgG+C3d	-	-	Pos IgG+C3d	-	Weak IgG	-
Eluate ID	-	-	Anti-A	-	Anti-A	-	-	-	-
Anti-A IgG titer	-	-	16	-	-	-	-	1	-
Anti-A IgM titer	-	-	8	-	-	-	-	1	-

d post-transpl: day after the patient’s renal transplant; PEX: plasma exchange; WBC: white blood cells; RBC: red blood cells; Hb: hemoglobin; Hct: hematocrit; MCV: mean corpuscular volume; PLT: platelets; BUN: blood urea nitrogen; GFR: glomerular filtration rate; LDH: lactate dehydrogenase; IAT: indirect antiglobulin test; DAT: direct antiglobulin test; ID: identity; IgG: immunoglobulin G; IgM: immunoglobulin M; Neg: negative; Pos: positive.

Figure 1.

Trend over time in markers of hemolysis (hemoglobin [Hb], direct and indirect bilirubin, lactate dehydrogenase [LDH])

DISCUSSION

PLS is a recognized complication of HSCT and solid organ transplantation involving ABO incompatibility. It occurs most frequently in group A recipients of group O grafts, the most common pairing of donor-recipient groups in the general population (approximately 44% of minor ABO mismatched transplants)⁵. This may relate to the higher antigenic density on A compared with non-A red blood cells. The hemolysis is mediated by donor-derived IgM and IgG anti-ABO antibodies that can induce complement system activation, although antibodies targeting antigens of other blood group systems (e.g., Rh, Kidd, Lewis) have also been reported^6–8. Risk factors for PLS include donor group O, previous sensitization and. in the recipient, immunosuppressive regimens less effective against B-cell proliferation (e.g., cyclosporine) or early post-transplant infections^9–11. Our patient never had these situations. Laboratory findings typically show a rapid decrease in hemoglobin levels, intravascular hemolysis (undetectable haptoglobin, increased lactate dehydrogenase, free hemoglobin in plasma and hemoglobinuria), and a positive DAT¹². The hemolysis is transient because donor B lymphocytes have a short lifespan (approximately 6–7 days), and their antibodies gradually wane as the cells die¹³. The median persistence of donor antibodies in renal transplant recipients is about 5 weeks¹⁴. The incidence and severity of hemolysis vary by organ, being lower in kidney transplants (ABO antibodies 17%, PLS 13%), higher in liver (ABO antibodies 40%, PLS 29%), and greatest in heart-lung transplants (ABO antibodies 70%, PLS 70%), likely reflecting the larger graft mass and lymphocyte burden^15,16.

Management includes maintenance of adequate renal perfusion and transfusion of components compatible with donor ABO type after pretransfusional tests, with particular attention to the critical role of serological cross-matching in the patient’s transfusion support. Studies recommend transfusing red blood cells of the same ABO group as that of the donor as long as a positive DAT and laboratory data indicative of ongoing active hemolysis persist. Once the disappearance of these conditions has been documented, the patient can be transfused with their own ABO group. Increasing corticosteroid doses often provide a rapid immunosuppressive effect¹⁷. In severe cases, PEX can effectively reduce antibody titers and circulating free hemoglobin, limiting further graft injury¹⁸. Outcomes are generally favorable in most cases, although rare instances of irreversible renal damage and graft loss have been reported^19,20. In the present case, the patient achieved a full recovery, with normalization of hematological and hemolytic indices.

CONCLUSIONS

This case underscores the importance of considering PLS in the differential diagnosis of moderate to severe hemolytic anemia occurring early after solid organ or HSCT transplantation, particularly in cases of minor ABO mismatch. A definitive diagnosis requires demonstration of donor-derived anti-A or anti-B antibodies bound to the recipient’s erythrocytes, identified through specific immunohematological testing (both O-type panel cells and A1-A2-B-Otype panel cells) and the exclusion of unexpected (and other) ABO antibodies. Management requires a multidisciplinary approach involving nephrology, hematology and transfusion medicine specialists. The syndrome is usually self-limiting, and treatment comprises transfusion of donor-type blood and optimization of immunosuppressive therapy. Patients should be advised upon discharge to promptly report dark-colored urine, which may signal early hemolysis. In our case, delayed recognition of such symptoms contributed to a postponed diagnosis. The Nephrology Transplantation Unit approved the routine inclusion of a DAT in early post-transplant monitoring, which could facilitate earlier detection of PLS and prevent severe anaemia, and the titration of ABO antibodies in the kidney donor in minor incompatibility. The DAT is a low cost, rapid, and easy to interpret test; if positive, confirmatory testing is part of standard transfusion laboratory practice. PEX, combined with corticosteroid boluses, can represent an effective therapeutic strategy in the early management of PLS.