Amelioration of Late Complications Following Unrelated Donor Bone Marrow Transplantation When Anti-Thymocyte Globulin Is Used as a Part of Conditioning.
Authors: Adess Matthew E. , Stiff Patrick , Rodriguez Tulio , Norton John , Parthasarthy Mala , Fox-Geiman Mary , Smith Scott , Toor Amir 
Published: October 2019

Abstract
Polyclonal anti-thymocyte globulin (ATG) reduces the risk for primary graft rejection as well as acute graft-versus-host disease (GVHD) by depleting T cells in both the host and the infused allograft. However, the impact of ATG on late outcomes is less certain. We report the results of a retrospective landmark analysis of consecutive patients who underwent an unrelated donor bone marrow transplant at our center between January 2001 and October 2005 (n=45) and survived at least 90 days following transplant. We compared late outcomes in patients who either recieved ATG (n=25) or did not (n=20) as a part of their conditioning regimen. Conditioning was with either busulfan and cyclophosphamide (n= 28; 17 without ATG) or BCNU, etoposide, cytarabine, and melphalan (n=18; 3 without ATG). Most patients (20) received rabbit ATG at a median dose of 3 mg/kg (range: 1.5–9 mg/kg) on day -4 and -3. Others were given equine ATG. GVHD prophylaxis consisted of tacrolimus + methotrexate in both groups. Median age was 42 years (range 18–65; 14 female). Bone marrow from unrelated donors matched at HLA-A, B, C, and DRB1 (7/8 and 8/8 matches) was used as the stem cell source. Diseases treated were CML (11), HD (9), AML (8), MDS (6), NHL (3), MM (3), and other (5). A median of 3 prior therapies had been given before transplant (range 1–5). There was no significant difference (Pearson χ2) in the number of patients beyond CR1/CP1 (n=25) and those having failed a prior autograft (n=17) between the two groups. The median overall survival in the recipients of ATG was 1382 days (95% CI: 373– 2391 days) as opposed to 364 days (95% CI: 0–851) in those not receiving ATG (P=0.125 by Log-Rank test); with a 1-year overall survival of 76% (59%–93%) vs. 50% (28–72) in the ATG vs. no ATG cohorts respectively, and 69% (49–89) vs. 44% (22–66) at 2-years. The 1-year progression free survival was 84% (69–98) vs.90% (77–100) in the ATG vs. no ATG cohorts, and 84% (69–98) vs. 67% (37–97) at 2 years. Chronic GVHD developed in 15/20 (75%) patients not receiving ATG (45% extensive), and in 12/25 (48%) in those recieving ATG (16% extensive) (P=0.06 Pearson χ2). Graft rejection was seen in 2/20 patients in the non-ATG arm and 1/25 patients in the ATG arm. Despite a lower incidence of chronic GVHD, the relapse rate was similar in the two groups (16% in the ATG group vs. 20% in the non-ATG group; P=0.73). Lymphoid recovery was similar in the two groups. The absolute lymphocyte counts at day-90 and day-180 post transplant were 680 vs 800/microL and 1100 vs. 1500/microL in the no ATG vs. ATG cohorts (P=0.275 repeated measures ANOVA). Serious late infections requiring parenteral antimicrobial treatment occured in 8 patients (32%) receiving ATG, and in 9 patients (45%) in the non-ATG arm ((P=0.248). CMV reactivation was seen in 8 patients (32%) receiving ATG, and 7 (35%) in the non-ATG arm. Eleven patients (55%) have died in the no ATG cohort from either relapse (2), GVHD (4) or infection (5); whereas in the ATG cohort 9 (36%) have died of either relapse (4), GVHD (3) or infection (2). In conclusion, ATG appears to reduce delayed transplant related complications, such as chronic GVHD and infections, in patients receiving bone marrow from unrelated donors. This may lead to a favorable trend towards improved survival in patients recieving ATG as a part of non-total body irradiation based conditioning.