CurrentCignaPolicy 0561

Thymus Tissue Transplantation

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Defines medical necessity and coverage criteria for thymus tissue transplantation (cultured thymus tissue/Rethymic) in pediatric patients and documents coding, background, and supporting evidence for Cigna-administered plans.

Policy Summary

PayerCigna

PolicyThymus Tissue Transplantation

Policy CodePolicy 0561

Change TypeNo material changes

Effective DateAug 15, 2026

Last ReviewAug 15, 2026

Next Review DateAug 15, 2027

Key ActionObtain prior authorization and submit required clinical documentation demonstrating congenital athymia and qualifying T‑cell/naive T‑cell counts before a single administration of cultured thymus tissue.

SourceLink

POLICY UPDATE CHANGES

No material clinical or coverage changes in this revision.

singlecovered dosing frequency when medically necessary

≤17 yrspopulation eligible for coverage

<50/mm3T‑cell threshold

105study population referenced

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CurrentCignaPolicy 0561

Thymus Tissue Transplantation

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Policy Summary

PayerCigna

PolicyThymus Tissue Transplantation

Policy CodePolicy 0561

Change TypeNo material changes

Effective DateAug 15, 2026

Last ReviewAug 15, 2026

Next Review DateAug 15, 2027

SourceLink

POLICY UPDATE CHANGES

No material clinical or coverage changes in this revision.

singlecovered dosing frequency when medically necessary

≤17 yrspopulation eligible for coverage

<50/mm3T‑cell threshold

105study population referenced

Coverage Criteria for Thymus Tissue Transplantation

inv-01: Initial Therapy - Medically Necessary Criteria

A single administration is considered medically necessary when ALL of the following are met:

Initial therapy criteria: a) Diagnosis of congenital athymia, including complete DiGeorge anomaly (cDGA) or FOXN1 deficiency; b) T‑cell count lower than 50/mm3 OR naive T‑cell count (CD3+CD4+CD45RA+CD62L+ or CD3+CD8+CD45RA+CD62L+) lower than 50/mm3; c) Absence of genetic defects associated with severe combined immunodeficiency (SCID)See individual nodes (T‑cell or naive T‑cell < 50/mm3)

Single administration

inv-02: Not Medically Necessary

Not medically necessary conditions: Thymus tissue transplantation is not medically necessary for all other indications, including but not limited to immune reconstitution in individuals with severe combined immunodeficiency (SCID) or partial DiGeorge Syndrome.

Applies to all other indications

Thymus tissue transplantation is covered only for pediatric patients (age ≤ 17 years) with a confirmed diagnosis of congenital athymia (including complete DiGeorge anomaly [cDGA] or FOXN1 deficiency) who meet the policy’s specific laboratory and genetic criteria. The policy explicitly states that thymus tissue transplantation is not medically necessary for indications other than pediatric congenital athymia — for example, it is not covered for immune reconstitution in individuals with severe combined immunodeficiency (SCID) or for patients with partial DiGeorge Syndrome.

Use of cultured thymus tissue for the purpose of immune reconstitution in individuals with SCID or partial DiGeorge syndrome is explicitly listed as not medically necessary. Providers should not request authorization or expect coverage for thymus tissue transplantation when the clinical indication is SCID or partial DiGeorge Syndrome, because these indications fall outside the policy’s covered population.

Candidate Eligibility Criteria

inv-16: Candidate criteria

Eligibility reflected from clinical trials and protocols:

Candidate eligibility: Diagnosis of complete DiGeorge anomaly (cDGA) or FOXN1 deficiency; profound T‑cell or naive T‑cell lymphopenia (typically <50/mm3); absence of genetic defects associated with SCID; clinical stability for surgery (no recent or imminent major cardiac surgery per trial exclusions); no active HIV infection, no ventilator dependence, and no CMV infection if immunosuppression is required.T‑cell or naive T‑cell < 50/mm3 (clinical trial threshold)

Based on clinical trial inclusion/exclusion criteria; some expanded access patients could have naive T‑cell >50/mm3

Evaluation and Diagnostic Requirements

Prior Authorization

Evaluation requirements — confirm diagnosis with SCID screen, flow cytometry, and genetic testing

Confirm diagnosis of congenital athymia prior to authorization and administration. This includes documentation of newborn SCID screening results and flow cytometry showing very low naive T‑cell counts (typically T‑cell or naive T‑cell counts < 50/mm3) and genetic testing to exclude defects associated with SCID (some protocols required two separate flow cytometry analyses: one within three months and one within one month before administration).

Newborn SCID screening indicating possible congenital athymia and confirmatory genetic testing to exclude SCID-associated defects.
Flow cytometry demonstrating very low naive T‑cell counts (CD3+CD4+CD45RA+CD62L+ or CD3+CD8+CD45RA+CD62L+) and/or total T‑cell count < 50/mm3.
If following protocols referenced in trials, provide two separate flow cytometry analyses (one within 3 months and one within 1 month before CTT administration).

Documentation Required

Contraindications and Exclusion Criteria

Clinical trial exclusion criteria inform the policy’s contraindication guidance. Examples of trial-based exclusions include: major cardiac surgery within four weeks prior to cultured thymus tissue (CTT) administration or anticipated within three months after CTT administration; patients judged to be poor surgical candidates by the surgeon or anesthesiologist; active HIV infection; ventilator dependence; and cytomegalovirus (CMV) infection in patients who would require immunosuppression. Prior attempts at immune reconstitution (for example prior HSCT or fetal transplant) were also exclusionary in the trials.

Provider Actions, Authorization, and Billing Guidance

Prior Authorization

Prior authorization required for thymus tissue transplantation

Prior authorization is required for a single administration of cultured thymus tissue when billed with unlisted CPT procedure codes or HCPCS unclassified biologics/drugs codes and the policy's medical necessity criteria must be met.

Relevant CPT unlisted codes: 27599, 60699.
Relevant HCPCS unclassified codes: C9399, J3490, J3590.

Step Therapy

Step therapy: none required; Rethymic is single‑administration biologic

No step therapy is specified for thymus tissue transplantation; Rethymic (cultured thymus tissue) is a single‑administration biologic product approved for congenital athymia.

Rethymic is processed, cultured donor thymus tissue implanted to support immune reconstitution and was approved by BLA in 2021.
Dosing is patient‑customized and delivered as a single administration in clinical studies.

Coding and Billing Codes

Considered Medically Necessary when criteria met - CPT (unlisted)CPTCovered

27599	Unlisted procedure, femur or knee
60699	Unlisted procedure, endocrine system

Considered Medically Necessary when criteria met - HCPCS (unclassified biologics/drugs)HCPCSCovered

C9399	Unclassified drugs or biologicals
J3490	Unclassified drugs
J3590	Unclassified biologics

Relevant ICD-10-CM diagnosis codesICD-10

D82.1	Di George's syndrome
Q89.2	Congenital malformations of other endocrine glands

Naive or total T-cell count threshold - policy values

Total T-cell count thresholdT-cell (total) count lower than 50/mm3

Naive CD4+ T-cell thresholdNaive T-cell (CD3+ CD4+ CD45RA+ CD62L+) count lower than 50/mm3

Naive CD8+ T-cell thresholdNaive T-cell (CD3+ CD8+ CD45RA+ CD62L+) count lower than 50/mm3

Alternative inclusion metricNaive CD3+ CD45RA+ CD62L+ count ≤ 5% of total T cells on two separate flow cytometry analyses (one within 3 months and one within 1 month before CTT) per trial protocols

Post-Transplant Monitoring and Coverage Notes

Immune reconstitution monitoring (flow cytometry, biopsies)

Recommended monitoring modalityPeripheral blood flow cytometry to assess naive and total T-cell counts (used in trial protocols and required for candidate evaluation)

Tissue-level monitoringThymic biopsies demonstrated thymopoiesis within ~2 months in clinical reports but are described in literature rather than as specified covered services in the policy

Frequency/Timing in protocolsSome protocols required two flow cytometry analyses (one within 3 months and one within 1 month before administration); post-transplant detection of naive T cells typically occurs ~3–5 months

Policy coverage noteImmune reconstitution monitoring (flow cytometry, biopsies) is described in supporting literature but is not specified as covered routine post‑transplant services in the policy

Definitions

CTT / Rethymic — definition and key facts

Product descriptionCultured thymus tissue (CTT), e.g., Rethymic: an allogeneic, processed and cultured postnatal donor thymus tissue product implanted to support immune reconstitution in pediatric patients with congenital athymia

Administration methodSurgical implantation of cultured thymus tissue slices into recipient quadriceps muscle (individual pockets in quadriceps), typically performed in the operating room

Regulatory status and dosingRethymic is FDA BLA‑approved for pediatric congenital athymia; dosing is patient‑customized based on slice surface area and patient body surface area; single administration was used in clinical studies

Congenital athymia — definition and related notes

DefinitionCongenital athymia: absence of a functioning thymus resulting in profound T‑cell and naive T‑cell deficiency (may be due to complete DiGeorge anomaly [cDGA] or FOXN1 deficiency)

Background and Clinical Context

Congenital athymia is a rare disorder characterized by absence or nonfunctional thymic tissue leading to profound deficiency of naive T cells and severe T‑cell lymphopenia. The policy references conditions commonly associated with congenital athymia, including complete DiGeorge anomaly (cDGA) and FOXN1 deficiency. Without immune reconstitution, affected infants typically experience life‑threatening immunodeficiency early in life; clinical series referenced in the policy report outcomes from cohorts of patients treated with cultured thymus tissue, with long‑term follow‑up (median up to 7.6–10.9 years) documenting survival and immune reconstitution in treated populations.

Policy Revision History

2026-08-15effective_dateLatest

Policy effective date set to 2026-08-15.

2026-08-15last_review

Policy last reviewed on 2026-08-15.

2027-08-15next_review

Next scheduled review on 2027-08-15.