**5. Desensitization regimens**

Desensitization aims to increase access to kidney transplantation in broadly sensitized individuals and to prevent ABMR after transplantation. In renal transplantation, desensitization could be done in a living or deceased donor setup. However, it is only performed in the deceased donor settings in heart and lung transplantation due to the nature of the donor and the organ transplanted.

In the living donor scenario, desensitization is planned well before surgery. In the deceased donor program, desensitization is attempted in the pre and peri-transplant period.

The desensitization protocols vary from center to center. Consensus is lacking on a standardized desensitization protocol among renal the transplant community. Most protocols use the following interventions in combinations (**Table 6**).

#### **5.1 Immunoglobulin (IVIG)**

IVIG predominantly contains IgG (90-99%) from pooled human plasma. The exact mechanism of action of IVIG is unknown; however, it exerts immunomodulatory effects via multiple pathways. It blocks the FC receptors on plasma cells, thus preventing the rebound of DSA. Furthermore, blocking the FC neonatal receptor increases the lysosomal degradation of the circulating IgG [29]. Some researchers previously reported hemolysis with high-dose IVIG administration [30]. It was linked with the presence of anti-A/B isohemagglutinins [31]. It led to improvements in IVIG manufacturing, and the modern formulations carry a low risk of hemolysis [32].

High-dose IVIG (2 g/kg) alone enabled renal transplantation in 13/15 highly sensitized patients in a study [33]. In another study, 2 g/kg IVIG was administered before and after renal and heart transplantation in 45 CDCXM positive candidates [34].


**Table 6.**

*Therapeutic agents for desensitization in renal transplantation.*

*Desensitization in Solid Organ Transplantation DOI: http://dx.doi.org/10.5772/intechopen.113262*

Crossmatch became negative in 35 cases and reduced to positive FCXM in the remaining seven candidates. Forty-two candidates were transplanted eventually. Acute rejection occurred in 31% of cases, and 7% lost graft. At 24 months, 89% had a functioning graft. Investigators from Cedar Sinai Center reported successful renal transplantation in highly sensitized candidates using high-dose IVIG and induction therapy [35, 37, 38]. Graft outcomes varied according to immunologic risk. Graft survival was 94–96% and 40–100% at 1 and 2 years, respectively. Fifteen to 35% of cases experienced ABMR.

A randomized trial of 48 sensitized individuals (PRA > 50%) compared high-dose IVIG for 4 months to placebo [39]. IVIG shortened the time to transplantation from 10.3 to 4.8 years. Thirty-five percent of candidates in the intervention group received transplants compared to 17% in the control group. Rejections occurred in 53% of cases in the IVIG group while 10% in the control group. Graft survival was 80% in the IVIG group and 75% in the control group at 30 months.

#### **5.2 Apheresis**

Apheresis has been part of desensitization regimens since the 1990s [40]. Apheresis removes preformed antibodies from the plasma. Various apheresis modalities are used in desensitization though the ideal apheresis technique in desensitization is not known yet. **Table 7** compares various apheresis modalities. A single-center, retrospective study looked at different apheresis modalities [41] in 45 DSA-positive renal transplant candidates. All modalities decreased DSA, but immunoadsorption (IA) and plasma exchange (PE) were more efficient than double filtration plasmapheresis (DFPP). DFPP is associated with severe adverse events, e.g., hypotension, high leukocyte counts, and low fibrinogen levels.

IA is frequently used in Europe, while PE is standard in the United States. Bleeding complications are more frequent with PE [42]. Giving time for fibrinogen to return to normal or repletion with cryoprecipitate before surgery reduces the risk of bleeding.

A retrospective case-control study compared desensitization with PE (1–12 sessions) + IVIG (100 mg/kg) in FCXM-positive renal transplant recipients to FCXMnegative controls [43]. Graft loss was high in the FCXM positive group at 9-year (14 vs. 7) [HR 2.6 (95% CI 1.03–6.4) t1/2 = 6.8 yr.] Graft survival at 1 and 5 years were 89.9 and 69.4% in the FCXM positive group compared to 97.6 and 80.6% in the control group. In conclusion, the medium- and long-term outcomes of positive FCXM living


#### **Table 7.**

*Comparison of plasmapheresis techniques.*


#### **Table 8.**

*Summary of study outcomes.*

kidney recipients are not promising. The results are comparable to extended criteria deceased donor renal transplantation.

A prospective study compared IVIG alone with two different combinations of PE, IVIG, and other interventions (**Table 8**) [44]. The author concluded that PE regimens result in lower ABMRs than IVIG-only regimens. Moreover, despite achieving a negative crossmatch, the rejection rate remained high in all the groups.

A pilot study analyzed the efficacy of two desensitization regimens in sensitized kidney transplant candidates who received deceased donor grafts [45]. The results (shown in **Table 9**) illustrate that intense immunosuppression on day 0 could improve long-term graft outcomes.

Another retrospective case-control study (n = 48) examined five desensitization protocols [46]. The participants were stratified into five based on the MFI levels of the immunodominant DSA. Acute ABMR (25 vs. 12.5%) and T cell mediate rejection (TCMR) (23 vs. 14%) were high in desensitized recipients. However, graft loss and patient survival were similar across the groups.

#### **5.3 Anti-CD-20 therapies**

Rituximab is a chimeric anti-CD20 monoclonal antibody. FDA initially approved it for lymphoma; however, it plays a role in autoimmune disorders and SOT. A combination of rituximab (1 gm on day 7 and 22) and high-dose IVIG (on day 0 and 30) showed a significant reduction in PRA (44 vs. 77%) in Phase I/II trial (n = 20) [38]. Although the ABMR rate was high at 31%, graft survival was 94% at 1 year.

In another study, the investigators desensitized 76 highly sensitized patients with rituximab and IVIG combination [37]. PRA declined significantly from 79.7 ± 25.6% to 67.1 ± 28.6% for class I and 59.7 ± 29.2% to 49.7 ± 27.8% for class II anti-HLA


**Table 9.** *Study result summary.*

*Desensitization in Solid Organ Transplantation DOI: http://dx.doi.org/10.5772/intechopen.113262*

antibodies. Fifty-nine percent of the participants received deceased donor kidney transplants. Graft survival was 84% at 24 months, but the ABMR rate was high at 37%.

A combination of rituximab and high-dose IVIG enabled renal transplantation in 71% of candidates in another study [47]. Transplantation with desensitization was more cost-effective than continuing dialysis.

A retrospective study compared desensitization with plasmapheresis and low-dose IVIG combination with or without rituximab (375 mg/m<sup>2</sup> ) [48]. The rebound of DSA and non-DSA anti-HLA antibodies were lower with the rituximab group (7 and 33% respectively) compared to the no rituximab group (32 and 55% respectively) at 1-month post-transplantation. However, rituximab did not alter the ABMR rate, 5-year allograft survival, and elimination of HLA antibodies.

A randomized control trial compared high-dose IVIG + rituximab (1 g) with high-dose IVIG + placebo in sensitized renal transplant candidates [49]. Six patients in the intervention and seven in the placebo arm received deceased donor kidney transplants. DSA levels at transplantation were not different, but ABMR was seen only in the placebo arm. No graft loss occurred in the rituximab arm compared to 2 in the placebo arm. The study was prematurely stopped due to poor outcomes in the placebo arm.

Obinutuzumab is a type II anti-CD20 monoclonal antibody used in refractory and relapsing hematological malignancies. It is more efficient than rituximab in depleting B-cells in lymphoid organs. An open-label phase I trial (n = 25) assessed the efficacy of obinutuzumab + IVIG (2 g/kg) in sensitized renal transplant candidates [50]. MFI levels decreased significantly but were clinically irrelevant. Nine patients developed severe adverse events, mainly infectious complications. Though encouraging, these results need further validation.

In summary, the combination of apheresis + IVIG and or B cell-depleting agent is the most used desensitization protocol in renal transplantation.

The exact sequence and doses of the desensitization therapies vary among the centers. We perform low and intermediate risk living donor HLAi incompatible renal transplants at our center. We do not perform CDCXM positive transplants. Low risk HLAi renal transplant candidates (DSA positive but negative FCXM) are desensitized with 1 gram/ kg single IVIG dose. Patients with intermediate risk HLAi renal transplants [DSA positive and FCXM positive (≤300 median channel shift)] receive a single dose of rituximab 500 mg IV with pre-medications a week before transplantation. Two doses of IVIG 1 gram/kg/day (max dose 140 gm) are administered on subsequent days. PE or IA is not used in HLAi transplant desensitization at our center. We do not repeat FCXM after desensitization therapy.

In deceased donor kidney transplantation, due to the unpredictable timing of the organ availability, pre-transplant desensitization is offered only to those within 1 year of receiving renal grafts. High-dose IVIG and rituximab are given in the same protocol as the living donors. Luminex single antigen testing is performed monthly to maintain the current sera for crossmatch testing. A second course of desensitization, consisting of PE sessions followed by high-dose IVIG and rituximab, is offered if a patient does not receive a transplant within six months. PE (1.5 plasma volume with 5% albumin replacement) is performed on alternate days. IVIG 2 gram/kg (maximum dose of 140 g) is delivered immediately following the last plasmapheresis session. Rituximab 375 mg/m2 is given one week after the last PE and IVIG session to avoid IVIG saturation of the Fc receptors [51]. This protocol is repeated every 6 months until the patient receives a transplant.

#### **5.4 Alternative approaches**

Bortezomib is a reversible proteasome inhibitor. It induces apoptosis of the differentiated plasma cells. A retrospective study of 44 sensitized patients (PRA > 20%) with positive CDCXM or a FCXM were desensitized with 1–2 cycles of bortezomib 1.3 mg/m2 (6–8 doses) + rituximab (375 mg/m2 ) and plasmapheresis [52]. Nineteen patients received kidney grafts from living donors. Immunodominant DSA declined 51.1% in 83% of the cases. ABMR rate was 12.5%, and graft survival was 94.7% at 1.2 yr.

In another study, 32 doses of bortezomib 1.3 mg/m<sup>2</sup> alone were administered for desensitization in 10 highly sensitized renal transplant candidates. Although MFI values declined after bortezomib, crossmatch, and cPRA remained unchanged [53]. Two patients discontinued therapy due to side effects and two had to reduce the dose.

Carfilzomib is an irreversible proteasome inhibitor. It has a sustained and durable effect on plasma cells compared to bortezomib. Furthermore, it has better tolerability than bortezomib. A combination of 12 escalating doses of carflizomib (20–32 mg/ m2 ) + PE (minimum three sessions) was trialed in 13 sensitized patients (mean PRA 97%) [54]. The immunodominant DSA declined by >50% in 70% of cases; however, the antibodies rebounded within 5 months after treatment discontinuation.

Eculizumab is a humanized monoclonal antibody against terminal complement component C5. It is used in ABMR treatment; however, experience in desensitization is limited. Thirty renal transplant candidates with initial B cell positive crossmatch (mean channel shift 200–450) were administered 1200 mg eculizumab immediately before transplantation, followed by 600 mg weekly dose for 4 weeks [55]. Patients with mean channel shift >300 were treated with plasmapheresis before transplantation to bring it down to <300. The outcomes were compared with a historical control who received the same desensitization protocol but without eculizumab. ABMR incidence was low in the eculizumab group, but the DSA rebounded.

A study compared the C1-inhibitor to placebo as a desensitization agent. Twenty highly sensitized patients (PRA > 50% and positive FCXM) who received plasmapheresis + rituximab + IVIG were randomized to C1-inhibitor or placebo [56]. ABMR was low in the intervention arm (20 vs. 30%, p = 0.6). Further validation is needed.

#### **5.5 Investigational agents**

Imlifidase is a recombinant IgG endopeptidase produced by *Streptococcus pyogenes*. It cleaves all sub-classes of IgG into Fc and F (ab) fragments. European Medicine Agency (EMA) has granted conditional approval for Imlifidase in desensitization, but the US Food and Drug Administration (FDA) is yet to approve it.

Two independent phase I/II studies (n = 25) were conducted in the United States and Sweden in highly sensitized patients (cPRA 96% and 81% respectively) [57]. Eight percent of participants had positive FCXM, and 92% had DSA. Imlifidase (0.24 mg/kg in the USA and 0.25 mg/kg or 0.5 mg/kg in Sweden) was given to all patients 4-6 hours pre-transplant. Ninety-two percent of the candidates received deceased donor kidney transplants. The United States cohort received a high dose IVIG, rituximab, and alemtuzumab at induction, while the Swedish population received horse ATG at induction but no IVIG and rituximab. IgG antibodies in the recipient serums were cleaved within 6 hours of the infusion and remained absent for at least 7 days. IgG recovered gradually but remained low at 28 days after the infusion.

#### *Desensitization in Solid Organ Transplantation DOI: http://dx.doi.org/10.5772/intechopen.113262*

DSA rebounded in the Swedish cohort between 7 and 14 days. In the United States cohort, DSA rebound was low. One patient from the US cohort had hyperacute rejection attributable to IgM DSA. The ABMR rate was 27% in the Swedish cohort at two weeks, while only 14% experienced ABMR at 2 and 5 months in the US cohort. Mean GFR at 1–6 months was 70 and 49 ml/min/1.73 m2 in the United States and Swedish cohorts, respectively.

Another multinational phase II study assessed the crossmatch conversion efficacy of Imlifidase in 19 highly sensitized kidney transplant candidates [58]. Eighty-nine percent (n = 17/19) of patients achieved a negative crossmatch within 24 hours of treatment. Thirteen patients received deceased donor kidney transplants, five received a living donor transplant, and one patient was not considered for transplantation due to a reaction to Imlifidase. DSA rebounded within 3–14 days after the treatment, though MFIs were lower than the pre-transplant level. Patient and graft survival at six months was 100% and 89%, respectively. Half of the patients experienced acute rejection; most (7/9) were ABMR.

A retrospective study examined 3 years of follow-up data of 39 crossmatch positive patients who received renal transplants [59]. Thirty-eight percent (n = 15/39) experienced ABMR. Overall graft survival was 84% at 3 years, notably lower in those who experienced ABMR (77 vs. 93%). Imlifidase has shown promising results, but further research is needed.

Clazakizumab- is a humanized, anti-interleukin (IL)-6 monoclonal antibody. It is used in chronic active ABMR in kidney transplantation, but experience as a desensitization agent is limited. Twenty highly sensitized patients (mean cPRA 96%) were desensitized with plasmapheresis, high-dose IVIG, and clazakizumab (25 mg \* 6 doses) in a pilot study [60]. Eighteen patients received deceased donor renal transplants. Clazakizumab was continued for 12 months post-transplantation. MFI levels declined in almost all patients. Rejection occurred in four cases; one graft was lost due to a technical problem. Patient survival was 100 percent at the end of the study. Further studies are needed to validate these findings.

Belimumab is a human monoclonal antibody that inhibits B cell activating factor. However, it failed to show notable results in a pilot study as a desensitization agent [61]. Similarly, Atacicept, another monoclonal antibody targeting B cell activating factor, did not achieve the desired results in pre-clinical desensitization studies [62, 63].

Daratumumab (anti-CD38 antibody) and anti-C-X-C chemokine receptor type 4 decreased DSA in animal models and improved graft survival [64]. Validation in clinical trials is awaited.

#### **5.6 Post renal transplant monitoring**

Monitoring protocols vary from center to center. Some centers monitor HLAi renal transplant recipients like HLA compatible patients but keep a low threshold for renal biopsy in case of graft dysfunction. Other centers prefer protocol renal biopsies at pre-defined time points. Most centers monitor DSA after HLAi transplantation, though the frequency of monitoring varies. In our center, DSA are monitored monthly for the first 3 months, every 3 months up to 12 months, and then yearly. IVIG given during the pre-conditioning therapy could show false positive DSA due to non-specific binding of IVIG to SAB, but this effect fades away after 2 months. Renal biopsy is performed in patients with persistent de novo DSA to rule out ABMR.
