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Patients will need to be monitored while their immune system begins to reconstitute. Here are monitoring recommendations and see the RETHYMIC® (allogeneic processed thymus tissue-agdc) prescribing information for further information.

How long does it take for RETHYMIC to work?

Immune reconstitution sufficient to protect from infection is unlikely to develop prior to 6-12 months after treatment with RETHYMIC5. For some patients elevated naïve T-cell numbers are not observed until 2 years after treatment. Supportive care measures should be continued until immune reconstitution is established.

What monitoring needs to be in place?

Monitoring should be performed regularly during the period the immune system is restored. T-cell counts should be checked by flow cytometry every 3 months and, as numbers rise, used to guide weaning of5:

  • Immunosuppression
  • Prophylaxis for pneumocystis
  • Reverse isolation

For additional information on monitoring, please see prescribing information.

When can the patient receive vaccines?

Immunizations should not be administered in patients who have received RETHYMIC until immune-function criteria have been met. Inactivated vaccines may be administered once all of the following criteria are met5:

  • Immunosuppressive therapies have been discontinued
  • Immunoglobulin (IgG) replacement therapy has been discontinued
  • The total CD4+ T-cell count is > 200 cells/mm3 and there are more CD4+ T-cells than CD8+ T cells (CD4+ > CD8+)
  • It is recommended that no more than 2 inactivated vaccines be given per month.

Live virus vaccines should not be administered until patients have met the criteria for inactivated vaccines and received vaccinations with inactivated agents (e.g. tetanus toxoid). No additional vaccines (live or inactivated), except the inactivated influenza vaccine, should be given within 6 months after vaccination with a measles-containing vaccine or within 2 months after the varicella vaccine.

Consider verifying response to vaccination with appropriate testing, in particular varicella and measles5.

When can my patient discontinue immunosuppresants?

Patients can be weaned off immunosuppression when at least 10% of CD3+ T-cells are naïve in phenotype3.

When can my patient discontinue IgG replacement therapy?

Patients should be maintained on immunoglobulin replacement therapy until all of the following criteria are met:

  • No longer on immunosuppression (at least 10% of CD3+ T cells are naïve in phenotype).
  • At least 9 months post-treatment.
  • Phytohemagglutinin (PHA) response within normal limits
  • Normal serum IgA is also desirable but not required.
  • Two months after stopping immunoglobulin replacement therapy, the IgG trough level should be checked.
  • If the IgG trough level is in the normal range for age, the patient can remain off of immunoglobulin replacement.
  • If the IgG trough level is lower than the normal range for age, immunoglobulin replacement therapy should be restarted and continued for a year before being retested using the above guidelines
When can my patient discontinue prophylaxis for pneumocystis?

Prior to and after treatment with RETHYMIC, patients should be maintained on Pneumocystis jiroveci pneumonia prophylaxis until all of the following criteria are met5:

  • No longer on immunosuppression (at least 10% of CD3+ T cells are naïve in phenotype).
  • At least 9 months post-treatment.
  • PHA response within normal limits.
  • CD4+ T-cell count > 200 cells/mm3.
How long should isolation continue?

As immunity builds and reaches thresholds for fighting off infection, you may guide families in ending strict isolation. Less restrictive isolation may continue as T-cell levels continue to rise and additional milestones are reached. Restrictive isolation may continue as T-cell levels continue to rise and additional milestones are reached5,7.

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Indication and Important Safety Information
IMPORTANT SAFETY INFORMATION

Immune reconstitution sufficient to protect from infection is unlikely to develop prior to 6-12 months after treatment with RETHYMIC. Given the immunocompromised condition of athymic patients, follow infection control measures until the development of thymic function is established as measured through flow cytometry. Monitor patients closely for signs of infection including fever. If a fever develops, assess the patient by blood and other cultures and treat with antimicrobials as clinically indicated. Patients should be maintained on immunoglobulin replacement therapy until specified criteria are met, and two months after stopping, IgG trough level should be checked. Prior to and after treatment with RETHYMIC, patients should be maintained on Pneumocystis jiroveci pneumonia prophylaxis until specified criteria are met.

RETHYMIC may cause or exacerbate pre-existing graft versus host disease (GVHD). Monitor and treat patients at risk for the development of GVHD. Risk factors for GVHD include atypical complete DiGeorge anomaly phenotype, prior hematopoietic cell transplantation (HCT) and maternal engraftment. GVHD may manifest as fever, rash, lymphadenopathy, elevated bilirubin and liver enzymes, enteritis, and/or diarrhea.

Autoimmune-related adverse events occurred in patients treated with RETHYMIC. These events included: thrombocytopenia, neutropenia, proteinuria, hemolytic anemia, alopecia, hypothyroidism, autoimmune hepatitis, autoimmune arthritis, transverse myelitis, albinism, hyperthyroidism, and ovarian failure. Monitor for the development of autoimmune disorders, including complete blood counts with differential, liver enzymes, serum creatinine, urinalysis, and thyroid function.

Pre-existing renal impairment is a risk factor for death.

In the clinical studies of RETHYMIC, 4 out of 4 patients with pre-existing cytomegalovirus infection died. The benefits/risks of treatment should be considered prior to treating patients with pre-existing CMV infection.

Because of the underlying immune deficiency, patients who receive RETHYMIC may be at risk of developing post-treatment lymphoproliferative disorder. Patients should be monitored for the development of lymphoproliferative disorder.

Transmission of infectious disease may occur because RETHYMIC is derived from human tissue and because product manufacturing includes porcine- and bovine-derived reagents.

Immunizations should not be administered in patients who have received RETHYMIC until immune-function criteria have been met.

All patients should be screened for anti-HLA antibodies prior to receiving RETHYMIC. Patients testing positive for anti-HLA antibodies should receive RETHYMIC from a donor who does not express those HLA alleles. HLA matching is required in patients who have received a prior HCT or a solid organ transplant. Patients who have received a prior HCT are at increased risk of developing GVHD after RETHYMIC if the HCT donor did not fully match the recipient.

Of the 105 patients in clinical studies, 29 patients died, including 23 deaths in the first year (< 365 days) after implantation.

The most common (>10%) adverse events related to RETHYMIC included: hypertension, cytokine release syndrome, rash, hypomagnesemia, renal impairment/failure, thrombocytopenia, and graft versus host disease.

To report suspected adverse reactions, please contact the FDA at 1-800-FDA-1088 or www.fda.gov/safety/medwatch.

INDICATION

RETHYMIC® (allogeneic processed thymus tissue–agdc) is indicated for immune reconstitution in pediatric patients with congenital athymia.

Limitations of Use:
RETHYMIC is not indicated for the treatment of patients with severe combined immunodeficiency (SCID).

REFERENCES

1. Collins C, Sharpe E, Silber A, Kulke S, Hsieh EWY. Congenital athymia: genetic etiologies, clinical manifestations, diagnosis, and treatment. J Clin Immunol. 2021;41(5):881-895. doi.org/10.1007/s10875-021-01059-7

2. Data on file, Enzyvant.

3. Markert ML, Gupton SE, McCarthy EA. Experience with cultured thymus tissue in 105 children. J Allergy Clin Immunol. Published online August 3, 2021. doi:10.1016/j.jaci.2021.06.028

4. Hsieh EWY, Kim-Chang JJ, Kulke S, Silber A, O’Hara M, Collins C. Defining the clinical, emotional, social, and financial burden of congenital athymia. Adv Ther. 2021;38(8):4271-4288. doi.org/10.1007/s12325-021-01820-9

5. RETHYMIC [package insert]. Cambridge, MA: Enzyvant Therapeutics, Inc; 2021.

6. Markert ML. Defects in thymic development. In: Sullivan KE, Stiehm ER, eds. Stiehm’s Immune Deficiencies. 2nd ed. New York, NY: Elsevier; 2020:357-379.

7. Gupton SE, McCarthy EA, Markert ML. Care of children with DiGeorge before and after cultured thymus tissue implantation. J Clin Immunol. 2021;41(5):896-905. doi.org/10.1007/s10875-021-01044-0

8. Markert ML, Devlin BH, Alexieff MJ, et al. Review of 54 patients with complete DiGeorge anomaly enrolled in protocols for thymus transplantation: outcome of 44 consecutive transplants. Blood. 2007;109(10):4539-4547.

9. Markert ML, McCarthy EA, Gupton SE, Lim AP. Cultured thymus tissue transplantation. In: Sullivan KE, Stiehm ER, eds. Stiehm's Immune Deficiencies. 2nd ed.: Academic Press; 2020:1229-1239.

Indication and Important Safety Information
IMPORTANT SAFETY INFORMATION

Immune reconstitution sufficient to protect from infection is unlikely to develop prior to 6-12 months after treatment with RETHYMIC. Given the immunocompromised condition of athymic patients, follow infection control measures until the development of thymic function is established as measured through flow cytometry. Monitor patients closely for signs of infection including fever. If a fever develops, assess the patient by blood and other cultures and treat with antimicrobials as clinically indicated. Patients should be maintained on immunoglobulin replacement therapy until specified criteria are met, and two months after stopping, IgG trough level should be checked. Prior to and after treatment with RETHYMIC, patients should be maintained on Pneumocystis jiroveci pneumonia prophylaxis until specified criteria are met.

RETHYMIC may cause or exacerbate pre-existing graft versus host disease (GVHD). Monitor and treat patients at risk for the development of GVHD. Risk factors for GVHD include atypical complete DiGeorge anomaly phenotype, prior hematopoietic cell transplantation (HCT) and maternal engraftment. GVHD may manifest as fever, rash, lymphadenopathy, elevated bilirubin and liver enzymes, enteritis, and/or diarrhea.

Autoimmune-related adverse events occurred in patients treated with RETHYMIC. These events included: thrombocytopenia, neutropenia, proteinuria, hemolytic anemia, alopecia, hypothyroidism, autoimmune hepatitis, autoimmune arthritis, transverse myelitis, albinism, hyperthyroidism, and ovarian failure. Monitor for the development of autoimmune disorders, including complete blood counts with differential, liver enzymes, serum creatinine, urinalysis, and thyroid function.

Pre-existing renal impairment is a risk factor for death.

In the clinical studies of RETHYMIC, 4 out of 4 patients with pre-existing cytomegalovirus infection died. The benefits/risks of treatment should be considered prior to treating patients with pre-existing CMV infection.

Because of the underlying immune deficiency, patients who receive RETHYMIC may be at risk of developing post-treatment lymphoproliferative disorder. Patients should be monitored for the development of lymphoproliferative disorder.

Transmission of infectious disease may occur because RETHYMIC is derived from human tissue and because product manufacturing includes porcine- and bovine-derived reagents.

Immunizations should not be administered in patients who have received RETHYMIC until immune-function criteria have been met.

All patients should be screened for anti-HLA antibodies prior to receiving RETHYMIC. Patients testing positive for anti-HLA antibodies should receive RETHYMIC from a donor who does not express those HLA alleles. HLA matching is required in patients who have received a prior HCT or a solid organ transplant. Patients who have received a prior HCT are at increased risk of developing GVHD after RETHYMIC if the HCT donor did not fully match the recipient.

Of the 105 patients in clinical studies, 29 patients died, including 23 deaths in the first year (< 365 days) after implantation.

The most common (>10%) adverse events related to RETHYMIC included: hypertension, cytokine release syndrome, rash, hypomagnesemia, renal impairment/failure, thrombocytopenia, and graft versus host disease.

To report suspected adverse reactions, please contact the FDA at 1-800-FDA-1088 or www.fda.gov/safety/medwatch.

INDICATION

RETHYMIC® (allogeneic processed thymus tissue–agdc) is indicated for immune reconstitution in pediatric patients with congenital athymia.

Limitations of Use:
RETHYMIC is not indicated for the treatment of patients with severe combined immunodeficiency (SCID).

REFERENCES

1. Collins C, Sharpe E, Silber A, Kulke S, Hsieh EWY. Congenital athymia: genetic etiologies, clinical manifestations, diagnosis, and treatment. J Clin Immunol. 2021;41(5):881-895. doi.org/10.1007/s10875-021-01059-7

2. Data on file, Enzyvant.

3. Markert ML, Gupton SE, McCarthy EA. Experience with cultured thymus tissue in 105 children. J Allergy Clin Immunol. Published online August 3, 2021. doi:10.1016/j.jaci.2021.06.028

4. Hsieh EWY, Kim-Chang JJ, Kulke S, Silber A, O’Hara M, Collins C. Defining the clinical, emotional, social, and financial burden of congenital athymia. Adv Ther. 2021;38(8):4271-4288. doi.org/10.1007/s12325-021-01820-9

5. RETHYMIC [package insert]. Cambridge, MA: Enzyvant Therapeutics, Inc; 2021.

6. Markert ML. Defects in thymic development. In: Sullivan KE, Stiehm ER, eds. Stiehm’s Immune Deficiencies. 2nd ed. New York, NY: Elsevier; 2020:357-379.

7. Gupton SE, McCarthy EA, Markert ML. Care of children with DiGeorge before and after cultured thymus tissue implantation. J Clin Immunol. 2021;41(5):896-905. doi.org/10.1007/s10875-021-01044-0

8. Markert ML, Devlin BH, Alexieff MJ, et al. Review of 54 patients with complete DiGeorge anomaly enrolled in protocols for thymus transplantation: outcome of 44 consecutive transplants. Blood. 2007;109(10):4539-4547.

9. Markert ML, McCarthy EA, Gupton SE, Lim AP. Cultured thymus tissue transplantation. In: Sullivan KE, Stiehm ER, eds. Stiehm's Immune Deficiencies. 2nd ed.: Academic Press; 2020:1229-1239.