Mixed chimerism after allogeneic hematopoietic stem cell transplantation for severe aplastic anemia

Figures & data

Table 1. The clinical characteristics of SAA patients (n=287).

Variables	N (%) ^a	Group 1, N (%)	Group 2, N (%)	Group 3, N (%)	Group 4, N (%)	P value
Age, y, mean ± SD	28 ± 12	28 ± 12	32 ± 13	26 ± 10	27 ± 5	0.242
Disease course m, median (range)	4 (1-305)	4 (1-305)	2 (1-48)	12 (1-242)	9 (1-248)	0.092*
Gender *						1.000
male	167 (58.2)	133 (79.6)	16 (9.5)	12 (7.1)	6 (3.5)
female	120 (41.8)	96 (80.0)	12 (10.0)	8 (6.6)	4 (3.4)
AA subtype*						0.017*
NSAA	5 (1.7)	5 (100%)	0 (0.0)	0 (0.0)	0 (0.0)
SAA	196 (68.3)	157 (80.1)	20 (10.2)	17 (8.7)	2 (1.0)
VSAA	86 (29.9)	67 (77.9)	8 (9.3)	3 (3.4)	8 (9.3)
IST before HSCT						0.300
yes	23 (8.0)	20 (86.9)	0 (0)	2 (8.6)	1 (4.3)
no	264 (92)	209 (79.1)	28 (10.6)	18 (6.8)	9 (3.4)
HLA matching						<0.001****
match	203 (70.7)	151 (74.3)	27 (13.3)	19 (9.3)	6 (2.9)
Mismatch (Haplo)	84 (29.3)	78 (92.8)	1 (1.1)	1 (1.1)	4 (4.7)
Conditioning regimen						<0.001****
CTX + ATG	28 (9.8)	12 (42.8)	10 (35.7)	5 (17.8)	1 (3.5)
FCA	111 (38.3)	86 (78.2)	11 (10.0)	10 (9.0)	4 (3.6)
BUCY + ATG (m)	67 (23.7)	56 (82.4)	6 (8.8)	4 (5.9)	1 (1.5)
BUCY + ATG (h)	81 (28.2)	75 (92.5)	1 (1.3)	1 (1.3)	4 (4.9)
ABO blood group						0.802
match	137 (47.7)	106 (77.3)	15 (10.9)	11 (8.0)	5 (3.6)
mismatch	150 (52.3)	123 (82.0)	13 (8.6)	9 (6.0)	5 (3.3)
Gender (REC / DON)						<0.001****
match	125 (43.6)	112 (89.6)	4 (3.2)	3 (2.4)	6 (4.8)
mismatch	162 (56.4)	117 (72.2)	24 (14.8)	17 (10.4)	4 (2.4)
Stem cell sources						0.060*
BM + PBSC	196 (68.3)	151 (77.0)	25 (12.7)	14 (7.1)	6 (3.0)
PBSC	91 (31.7)	78 (85.7)	3 (3.2)	6 (6.5)	4 (4.3)
TBI before HSCT						0.451
yes	17 (5.9)	15 (88.2)	0 (0.0)	1 (5.8)	1 (5.8)
no	270 (94.1)	214 (79.2)	28 (10.3)	19 (7.0)	9 (3.3)
Type of donor						<0.001****
matched sibling	112 (39.0)	73 (65.2)	24 (21.4)	13 (11.6)	2 (1.8)
unrelated	91 (31.7)	78 (85.7)	3 (3.3)	6 (6.6)	4 (4.4)
haploidentical	84 (29.3)	78 (92.8)	1 (1.2)	1 (1.2)	4 (4.8)
Death or Secondary transplantation						<0.001****
yes	32 (11.1)	19 (59.4)	1 (3.1)	2 (6.3)	10 (32.2)
no	255 (88.9)	210 (82.4)	27 (10.6)	18 (7.0)	0 (0.0)

^a Unless specifically mention; * Due to rounding, not all percentages total 100%.

ATG, anti-thymocyte globulin; BM, bone marrow; BUCY, busulfan + cyclophosphamide; DON, donor; CTX, cyclophosphamide; FCA, fludarabine + cyclophosphamide + anti-thymocyte globulin; HLA, human leukocyte antigen; HSCT, hematopoietic stem cell transplantation; IST, immunosuppressive therapy; PBSC: peripheral blood stem cell; Group 1: Donor chimerism (DC); Group 2: mixed chimerism (MC) without cytopenia; Group 3: MC with cytopenia; Group 4: secondary graft failure (SGF); TBI, total Body Irradiation; REC, receptor; SD, standard deviation; * P < 0.1; *** P < 0.01; **** P < 0.001. The BuCy + ATG(m) regimen is used for matched transplantation, while the BuCy + ATG(h) regimen is used for haploidentical transplantation.

Figure 1. Frequency and outcome of mixed chimerism (MC) based on (A) time of onset and (B) initial MC levels. Level 1, <10%residual host cells (RHCs); level 2, 10-25% RHCs; level 3, >25% RHCs. Dynamic changes in MC were monitored. The left panel of Figure 1(B) shows the initial MC levels and the right panel the final MC level. In Figure 1(B), the left side of picture B is the initial chimerism when MC appeared, we tracked the dynamic changes of chimerism of these patients. The right side of the picture shows the final outcome of chimerism.

Figure 2. Prognostic analysis of aplastic anemia (AA)patients with different chimerism statuses following allogeneic hematological stem cell transplantation (allo-HSCT). (A) Distribution of survival time (left panel) and curves (right panel) of AA patients. (B) restricted mean survival time (RMST) of patients with severe aplastic anemia (SAA) with different chimerism statuses following allo-HSCT. Group 1, donor chimerism (DC); group 2, mixed chimerism (MC) without cytopenia; group 3, MC with cytopenia; group 4, secondary graft failure (SGF). OS, overall survival.

Table 2. Risk factors for MC patients without transfusion dependence.

Variables	Group 1/2, N	Univariate logistic regression			Multivariate logistic regression
		OR	95% CI	P value	OR	95% CI	P value
Age, y
<20y	54/6	1.000	Referent
20-40y	136/12	0.794	0.284-2.223	0.661
>40y	39/10	2.308	0.774-6.882	0.134
Disease course, m
<6m	122/22	1.000	Referent
6m-1y	39/4	0.665	0.215-2.056	0.479
>1y	68/2	0.176	0.040-0.773	0.021**
Gender
male	133/16	1.000	Referent
female	96/12	0.962	0.425-2.127	0.925
AA subtype
SAA	162/20	1.000	Referent
VSAA	67/8	1.034	0.434-2.463	0.940
IST before HSCT
yes	20/0	0.000	0.000	0.998
no	209/28	1.000	Referent
HLA matching
match	157/27	1.000	Referent
mismatch	78/1	0.072	0.010-0.538	0.010**
Conditioning regimen
CTX + ATG	12/10	1.000	Referent
FCA	86/11	0.153	0.054-0.438	<0.001****	0.340	0.111-1.042	0.059*
BUCY + ATG(m)	56/6	0.129	0.039-0.422	0.001***	0.277	0.079-0.975	0.046**
BUCY + ATG(h)	75/1	0.016	0.002-0.137	<0.001****	0.220	0.002-0.189	0.001***
ABO blood group
match	106/15	1.000	Referent
mismatch	123/13	0.747	0.340-1.640	0.467
Gender (REC / DON)
match	112/4	1.000	Referent
mismatch	117/24	5.744	1.932-17.079	0.002***	3.860	1.227-12.144	0.021**
Stem cell sources
BM + PBSCs	151/25	1.000	Referent
PBSCs	78/3	0.232	0.068-0.793	0.020**	0.177	0.049-0.643	0.009***
TBI before HSCT
yes	15/0	0.000	0.000	0.999
no	214/28	1.000	Referent
Type of donor
matched sibling	73/24	1.000	Referent
unrelated	78/3	0.117	0.034-0.405	0.001***
haploidentical	78/1	0.039	0.005-0.296	0.002***

* P < 0.1; ** P < 0.05; *** P < 0.01; **** P < 0.001.

Table 3. Risk factors for MC patients with transfusion dependence.

Variables	Univariate logistic regression			Multivariate logistic regression
	OR	95% CI	P value	OR	95% CI	P value
Age, y, (n)
<20y	1	Referent
20-40y	0.794	0.284-2.223	0.661
>40y	0.462	0.088-2.409	0.359
Disease course m, median (range)
<6m	1.000	Referent
6m-1y	1.341	0.331-5.435	0.681
>1y	2.563	0.933-7.040	0.068*
Gender
male	1.000	Referent
female	0.924	0.364-2.346	0.867
AA subtype
SAA	1.000	Referent
VSAA	0.427	0.121-1.504	0.185
IST before HSCT
no	1.000	Referent
yes	1.161	0.251-5.369	0.848
HLA matching
match	1.000	Referent
Mismatch (Haplo)	0.102	0.012-0.775	0.027**
Conditioning regimen
CTX + ATG	1.000	Referent
FCA	0.279	0.081-0.956	0.042**	0.350	0.099-1.234	0.102
BUCY + ATG(m)	0.171	0.040-0.735	0.018**	0.230	0.052-1.018	0.053*
BUCY + ATG(h)	0.032	0.003-0.298	0.003***	0.470	0.005-0.446	0.008***
ABO blood group
match	1.000	Referent
mismatch	0.705	0.281-1.767	0.456
Gender (REC / DON)
match	1.000	Referent
mismatch	5.425	1.547-19.017	0.008***	4.111	1.142-14.793	0.030**
Stem cell sources
BM + PBSCs	1.000	Referent
PBSCs	0.830	0.307-2.243	0.713
TBI before HSCT
no	1.000	Referent
yes	0.751	0.094-5.998	0.787
Type of donor
matched sibling	1.000	Referent
unrelated	0.432	0.156-1.196	0.106
haploidentical	0.072	0.009-0.564	0.012**

* P <  0.1; **P <  0.05; ***P <  0.01.

Figure 3. Therapeutic effect of patients with MC with cytopenia or SGF following allo-HSCT. (A) Patient response to different treatments. (B) Patient response to increase immunosuppressant intensity and cellular therapy. donor stem cell infusion (DSI), mesenchymal stem cell (MSC) and umbilical cord blood stem cell (UCB) were part of cellular therapy. Inside circle, cellular therapy; outside circle, increase immunosuppressant intensity.