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Our Science

Prior to development of TruGraf®, a surveillance biopsy performed on a patient with stable renal function was the only way to identify or rule out the presence of subclinical acute rejection.

TruGraf intro stain

Post-transplant patient monitoring has typically involved testing for immunosuppressive drug levels which really only indicate whether patients are taking medications as prescribed or not, and measuring serum creatinine levels. While creatinine is an excellent indicator of renal function, it’s a late trailing indicator of damage already done to the graft as 50% of kidney function may be lost before serum creatinine goes up.

TruGraf Intro graph

Early studies ignored the prevalence of borderline rejection in protocol biopsies. Recent studies (1. Friedewald, et al. 2018) and several additional studies (2,3,4,5) demonstrated that.

  • subclinical acute rejection is prevalent in 25% of patients histology is characterized as Borderline in 80% of these cases
  • patients with subclinical acute rejection can develop chronic rejection and IFTA and potentially graft loss
  • patients with subclinical acute rejection have worse outcomes, if untreated

Benefits of TruGraf®

The TruGraf® test is a minimally-invasive test that measures differentially expressed genes in the blood of renal transplant recipients to identify patients who are likely to be adequately immunosuppressed and in doing so rule out subclinical acute rejection. TruGraf® uses RNA microarray technology to determine whether a patient’s blood gene expression profile is more similar to that obtained from a reference population classified by simultaneous histological analysis of a biopsy as Transplant eXcellence (TX), and likely adequately immunosuppressed, or not-TX, and likely to be inadequately immunosuppressed.

Intended Use

The TruGraf® test is intended for use in kidney transplant recipients with stable renal function as an alternative to surveillance biopsies.

Indications for Use

TruGraf® is indicated for use in renal transplant patients who are 18 years of age or older and at least 90 days post-transplant with stable serum creatinine values (current serum creatinine <2.3 mg/dl, <20% increase compared to the average of the previous 3 serum creatinine levels). Clinical validity of the TruGraf® test was established in kidney transplant recipients (First et al, 2017).

Patients who meet all of the following criteria are eligible for TruGraf® testing:

  • Males or females of at least 18 years of age.
  • Recipient of a primary or subsequent deceased-donor or living-donor kidney transplantation.
  • Stable serum creatinine (current serum creatinine <2.3 mg/dl, <20% increase compared to the average of the previous 3 serum creatinine levels)
  • Kidney transplant patients who are more than 90 days post-transplant

Contraindications and Limitations:

TruGraf® has not yet been evaluated in patients who are:

  • Recipients of a combined organ transplantation with an extra-renal organ and/or islet cell transplant.
  • Recipients of previous non-renal solid organ and/or islet cell transplantation.
  • Infected with HIV.
  • Patients with BK nephropathy.
  • Patients that have nephrotic proteinuria (urine protein >3 gm/day).

Limitations:

  • The performance and clinical utility of TruGraf® have been established in a cross sectional study (i.e., single point in time) at transplant centers utilizing surveillance biopsies. Clinical utility of TruGraf® at centers not utilizing surveillance biopsies is currently being investigated.
  • A TruGraf® test result of TX does not guarantee adequate immunosuppression. Patients with a TX TruGraf® test result should be advised to continue monitoring as per their local standard of care and clinical assessment.
  • TruGraf® may produce false negative or false positive results. A false positive result occurs when TruGraf® produces a not-TX result, even though a biopsy will not find evidence of immune activation. A false negative result occurs when TruGraf® produces a TX result, even though a biopsy will identify evidence of immune activation.

Clinical Evidence

TruGraf® rules out silent subclinical rejection in patients with stable renal function. Noninvasive blood or urine based biomarkers for renal graft rejection have been investigated for many years. To date, only TruGraf® has been validated as having clinical utility for surveillance of kidney transplant recipients with stable renal function, providing a non-invasive means of assessing whether such a patient is adequately immunosuppressed, without the potential harm and cost of performing biopsies. The analytical validation (9) and list of genes used as classifiers based on a Random Forest model (10) have been reported for TruGraf®. Recently, an external clinical validation from seven transplant centers defined the key clinical performance parameters for this assay (11), as summarized in Table 1 and Figure 1. In this study, the high negative predictive value (NPV) of TruGraf® was demonstrated in clinical use, making it a strong rule-out test. Over 90% of stable patients who received a “TX” (“Transplant eXcellence”; negative) result were confirmed to have an immune quiescent phenotype, meaning that a physician can have a high degree of confidence that a patient who tests as “TX” does not harbor silent subclinical rejection. Importantly this study also found that up to 65% of surveillance biopsies could be avoided in the cohort tested. Unpublished data involving analysis of an additional 129 biopsy-confirmed blood samples provided by Northwestern University (originally used for the CTOT-08 study) revealed identical performance metrics for TruGraf® (NPV of 90%). A fourth publication described the impact of TruGraf® results on physician decision making for clinical decisions (12). This study highlighted the high degree of confidence physicians place on the ability of TruGraf® to provide valuable, added information that could lead to avoidance of unnecessary surveillance biopsies as summarized in Table 2.

Table 1. Summary of TruGraf® performance characteristics in a multicenter, observational study (Marsh et al., 2019)

TruGraf® Clinical Evidence Table 1.

table 1

Table 2: Responses from Principal Investigators to Prospective and Retrospective Questionnaires (First et al., 2019)

TruGraf® Clinical Evidence Table 2.

table 2

TruGraf® Clinical Evidence Figure 1.

Individual Site Accuracy of TX Result chart

What Makes TruGraf® a Good Biomarker to Rule Out Subclinical Acute Rejection?

  • 107 Genes (mRNA) related to inflammation pathways
  • 91% NPV
  • 94% Concordance with biopsy
  • Risk stratification of patient population to provide comfort to those in whom silent rejection is confidently ruled out, and enable clinicians to focus on those that likely need closer attention

References:

  1. Friedwald JJ, et al., Development and clinical validity of a novel blood-based molecular biomarker for subclinical acute rejection following kidney transplant, American Journal of Transplantation, July 2019, 98-109.
  2. Primary research study by CLINICevAL Solutions, LLC, 2019
  3. First MR, Pierry D, McNulty M, Kurian SM, Rose S, Whisenant T, et al. Analytical performance validation of a molecular diagnostic signature in kidney transplant recipients. J Transplant Technol Res 2017;7:176. https://doi. org/10.4172/2161-0991.1000176.
  4. First MR, Peddi VR, Mannon R, et al. Investigator Assessment of the Utility of the TruGraf Molecular Diagnostic Test in Clinical Practice. Transplantation Proceedings, 2019, 51, 729-733. https://doi.org/10.1016/j.transpro¬ceed.2018.10.024.
  5. Marsh C, Kurian SM, Rice J, et al. Application of TruGraf® v1: A Novel Molecular Biomarker for Managing Kidney Transplant Recipients with Stable Renal Function. Transplantation Proceedings. April 2019; Epub 26, January 2019.
  6. Local Coverage Determination MolDX: TruGraf Blood Gene Expression Test (DL38039). Effective Date of Reimbursement: 25, November, 2019 from cms.gov.