Can we start antithymocyte globulin (aTT) if the bone marrow (BM) aspirate has Langerhans cells?

Antithymocyte Globulin (ATG) Treatment in the Presence of Langerhans Cells in Bone Marrow Aspirate

ATG therapy can be initiated in patients with Langerhans cells in the bone marrow aspirate, as the presence of these cells is not a contraindication to treatment. The decision should be based on the primary diagnosis and indication for ATG rather than the incidental finding of Langerhans cells.

Understanding Langerhans Cells in Bone Marrow

• Langerhans cells can occasionally be found in bone marrow aspirates, typically in very small numbers (usually <10-20 cells per slide or <0.5% of leukocytes) 1
• Their presence alone does not indicate a contraindication to ATG therapy 1
• CD1a staining by immunocytochemistry is the most reliable method to identify Langerhans cells in bone marrow samples 1

ATG Therapy Considerations

Mechanism of Action

• ATG works primarily through immunosuppressive effects on lymphocytes, particularly CD8+ T cells that may have suppressive activity on hematopoietic progenitor cells 2
• The therapeutic effect is not directly related to or impacted by the presence of Langerhans cells 2

Clinical Applications of ATG

• ATG is commonly used in conditions such as aplastic anemia, where it suppresses abnormal immune responses that inhibit hematopoiesis 3
• Horse ATG has shown superior remission rates compared to rabbit ATG in treatment-naïve aplastic anemia 4
• In hypoplastic myelodysplastic syndrome (MDS), immunomodulatory treatment with ATG may be offered, though with limited success 5

Monitoring During ATG Treatment

• Before initiating ATG therapy:

  • Complete baseline bone marrow assessment including morphology, cytogenetics, and flow cytometry 5
  • Assess for any active infections that could be exacerbated by immunosuppression 5

• During treatment:

  • Monitor for response through serial peripheral blood counts and repeat bone marrow examinations 5
  • Assess for treatment-related complications such as serum sickness, infections, or cytokine release syndrome 3

Special Considerations

• In patients with suspected Langerhans cell histiocytosis (LCH), ATG has shown limited efficacy (only 15% response rate) 6
• The combination of ATG with cyclosporine has demonstrated better outcomes in aplastic anemia than ATG alone 3
• Response to ATG therapy should be evaluated based on standard response criteria for the primary condition being treated 5

Conclusion

The presence of Langerhans cells in bone marrow aspirate should not prevent the use of ATG therapy when clinically indicated. Treatment decisions should be based on the primary diagnosis and standard protocols for that condition rather than this incidental finding.