The Detection of ANTI-Platelet Factor 4 /Heparin Antibodies during the Post Chirurgical Period of LUNG Transplantation Is Associated with a Higher Frequency of ACUTE Cellular Rejection

Background: Heparin-induced thrombocytopenia (HIT) is characterized by the presence of antibodies directed against a complex of Platelet Factor 4 and heparin (PF4/H). These antibodies usually appear within 3 to 6 days after the beginning of heparin therapy, belong predominantly to IgG isotype, and activate platelets, leading to a thrombotic tendency.

Aims: To analyze prospectively the incidence of PF4/H Ab in patients with bipulmonary transplantation (BPT) and to identify a possible consequence of the presence these antibodies on thrombotic events and graft dysfunction.

Patients & Methods: Citrated blood samples of 85 consecutive patients (median age 37 years, range : 15-65) with BTP [51 (60 %) cases of cystic fibrosis (CF), 34 (40 %) cases of chronic obstructive pulmonary disease (COPD)] were analyzed on a first sample before the transplantation (D0) and on a second sample collected within 10 and 17 days after the surgery [median level: 13 days, range : 7 - 17). A third sample was analysed at least 3 months later in case of positivity of PF4/H Ab. For 12 patients, extracorporeal membrane oxygenation (ECMO) was needed up to 10 post-operative days. Patients were treated at least by a triple immunosuppressive regimen (tacrolimus, mycophenolic acid and corticosteroids) and usually by a low molecular weight heparin. PF4/H Ab were detected using ELISA (Asserachrom HPIA, Diagnostica Stago, France). Bronchoscopic transbronchial biopsies (BTB) were performed 10 days after the surgery, then every month during the first year of follow-up (FU). Acute cellular rejection (ACR) is defined by perivascular or peribronchiolar lymphocytic infiltrates in the absence of infection and are expressed as grade A0 (none), grade A1 (minimal), grade A2 (mild), grade A3 (moderate) and qrade A4 (severe). As recommended, in order to quantify the ACR intensity during first year after BPT, we summed the numbers characterizing the intensity of the rejection.

Results: Eight patients (9.4 %) had PF4/H Ab at D0, which were either IgA or IgM,but not of IgG subtype. In 5 cases, the antibodies remaind present on the post-surgical sample. One patient had a plasma exchange the day before the post surgical sample and was excluded. Presence of PF4/H Ab was observed in 27 cases (32.1%) on the second sample, but disappeared in all cases on the third sample. The duration of the surgery was similar in both group, as well as the use of post-surgical ECMO. Frequency of PF4/H Ab was similar in patients with CF or COPD. PF4/H Ab were of IgG isotype in 52.2% of cases. Seventeen-patients (21.5 %) experienced a thrombotic event within the 3 months following the BPT: 8 of them (29.6 %) had PF4/H Ab, this was not significantly different from the frequency of PF4/H Ab in patients without thrombosis (17.3 %, p = 0.33). Because of frequent pulmonary infections, median leucocyte count was increased at D0 in patients with PF4/H Ab (12.5 x10⁹/L) as well as in patients without these antibodies (10.9 x10⁹/L), and remained elevated on the second sample (respectively 12.7 and 13.4 x10⁹/L), but there was no significant differences between patients with or without PF4/H Ab. Platelet counts were not different at D0 between both groups (median 304 x10⁹/L for patients with PF4/H Ab versus 300 x10⁹/L for patients without PF4/H Ab) but during the FU, patients with PF4/H Ab had a median level of platelets (515 x10⁹/L) significantly higher (p = 0,034) than patients without PF4/H Ab (429 x10⁹/L). Lastly, tacrolimus levels were not significantly different in both group of patients (6.8 ng/mL in patients with PF4/H Ab versus 6.7 ng/mL in patients without PF4/H Ab) making unlikely an insufficient immunosuppression in patients with PF4/H Ab. A one-year FU was obtained for 73 patients. Eighteen patients (69.2%) with PF4/H Ab presented at least one episode of ACR versus 40.4% in patients without PF4/H Ab (p = 0.035). In addition, the mean score of ACR (indicating the severity or the repetition of the ACR) was significantly (p = 0.02) higher in patients with PF4/H Ab than in patients without PF4/H Ab (1.21 versus 0.59).

Conclusion: As for cardiac or hepatic transplantations, despite a strong immunosuppressive regimen, a high frequency of transient PF4/H Ab is observed in patients undergoing BLT. Their appareance is not related to thrombocytopenia and/or thrombotic events. However, they could be an early marker of a cellular reaction againts the graft.