Kite and Humanigen Announce Clinical Collaboration to Evaluate Investigational Combination of Yescarta® (Axicabtagene Ciloleucel) with Lenzilumab in Relapsed/Refractory Diffuse Large B-Cell Lymphoma

— Phase 1/2 Multi-Center Clinical Trial to Begin Enrolling in Q4
2019 —

SANTA MONICA, Calif. & BURLINGAME, Calif.–(BUSINESS WIRE)–Kite, a Gilead Company (Nasdaq: GILD), and Humanigen, Inc. (HGEN) announced
today the formation of a clinical collaboration to conduct a Phase 1/2
study of lenzilumab, an investigational anti-GM-CSF monoclonal antibody,
with Yescarta^® (axicabtagene ciloleucel) in patients with
relapsed or refractory diffuse large B-cell lymphoma (DLBCL). The
objective of this study is to determine the effect of lenzilumab on the
safety of Yescarta. Kite will act as the sponsor of this study and will
be responsible for its conduct.

GM-CSF has been identified, through clinical correlative analysis and
preclinical modeling, as a potential key signal in the inflammatory
cascade triggering toxicities associated with chimeric antigen receptor
T (CAR T) cell therapy.¹ Toxicities associated with CAR T
therapy include neurologic toxicity and cytokine release syndrome (CRS).
Emerging pre-clinical evidence suggests that lenzilumab inhibition of
GM-CSF may have the potential to disrupt CAR T cell mediated
inflammation without disrupting CAR T cell anti-tumor efficacy.

“CAR T therapy represents a significant advance in the way relapsed or
refractory large B-cell lymphoma is treated,” said John McHutchison, AO,
MD, Chief Scientific Officer, Head of Research and Development, Gilead.
“As leaders in cell therapy, we are committed to pursuing a number of
clinical and preclinical strategies aimed at further improving the
efficacy and safety of CAR T therapy. We look forward to this clinical
collaboration with Humanigen and to evaluating the combination of
lenzilumab and Yescarta in our clinical trial.”

“Humanigen has pioneered the approach to neutralizing GM-CSF to improve
CAR T,” said Cameron Durrant, MD, Chief Executive Officer, Humanigen.
“This collaboration with Kite will help validate the work Humanigen has
done in understanding the pathophysiology of the inflammatory cascade as
well as the potential role GM-CSF plays in influencing CAR T cell
treatment outcomes.”

Yescarta was the first CAR T cell therapy to be approved by the U.S.
Food and Drug Administration (FDA) for the treatment of adult patients
with relapsed or refractory large B-cell lymphoma after two or more
lines of systemic therapy, including DLBCL not otherwise specified,
primary mediastinal large B-cell lymphoma, and high grade B-cell
lymphoma and DLBCL arising from follicular lymphoma. Yescarta is not
indicated for the treatment of patients with primary central nervous
system lymphoma. The Yescarta U.S. Prescribing Information has a BOXED
WARNING for the risks of cytokine release syndrome and neurologic
toxicities; see below for Important Safety Information.

Lenzilumab, alone or in combination with other therapies such as
Yescarta, is investigational and has not been approved by the FDA or any
regulatory authority for any uses. Efficacy and safety have not yet been
established.

Stifel, Nicolaus & Company, Incorporated acted as exclusive financial
advisor to Humanigen in this transaction.

U.S. Important Safety Information for Yescarta

BOXED WARNING: CYTOKINE RELEASE SYNDROME AND NEUROLOGIC
TOXICITIES

• Cytokine Release Syndrome (CRS), including fatal or
  life-threatening reactions, occurred in patients receiving Yescarta.
  Do not administer Yescarta to patients with active infection or
  inflammatory disorders. Treat severe or life-threatening CRS with
  tocilizumab or tocilizumab and corticosteroids.
• Neurologic toxicities, including fatal or life-threatening
  reactions, occurred in patients receiving Yescarta, including
  concurrently with CRS or after CRS resolution. Monitor for neurologic
  toxicities after treatment with Yescarta. Provide supportive care
  and/or corticosteroids as needed.
• Yescarta is available only through a restricted program under a
  Risk Evaluation and Mitigation Strategy (REMS) called the Yescarta
  REMS.

CYTOKINE RELEASE SYNDROME (CRS): CRS occurred in 94% of patients,
including 13% with ≥ Grade 3. Among patients who died after receiving
Yescarta, 4 had ongoing CRS at death. The median time to onset was 2
days (range: 1-12 days) and median duration was 7 days (range: 2-58
days). Key manifestations include fever (78%), hypotension (41%),
tachycardia (28%), hypoxia (22%), and chills (20%). Serious events that
may be associated with CRS include cardiac arrhythmias (including atrial
fibrillation and ventricular tachycardia), cardiac arrest, cardiac
failure, renal insufficiency, capillary leak syndrome, hypotension,
hypoxia, and hemophagocytic lymphohistiocytosis/macrophage activation
syndrome. Ensure that 2 doses of tocilizumab are available prior
to infusion of Yescarta. Monitor patients at least daily for 7 days at
the certified healthcare facility following infusion for signs and
symptoms of CRS. Monitor patients for signs or symptoms of CRS for 4
weeks after infusion. Counsel patients to seek immediate medical
attention should signs or symptoms of CRS occur at any time. At the
first sign of CRS, institute treatment with supportive care, tocilizumab
or tocilizumab and corticosteroids as indicated.

NEUROLOGIC TOXICITIES: Neurologic toxicities occurred in 87% of
patients. Ninety-eight percent of all neurologic toxicities occurred
within the first 8 weeks, with a median time to onset of 4 days (range:
1-43 days) and a median duration of 17 days. Grade 3 or higher occurred
in 31% of patients. The most common neurologic toxicities included
encephalopathy (57%), headache (44%), tremor (31%), dizziness (21%),
aphasia (18%), delirium (17%), insomnia (9%) and anxiety (9%). Prolonged
encephalopathy lasting up to 173 days was noted. Serious events
including leukoencephalopathy and seizures occurred with Yescarta. Fatal
and serious cases of cerebral edema have occurred in patients treated
with Yescarta. Monitor patients at least daily for 7 days at the
certified healthcare facility following infusion for signs and symptoms
of neurologic toxicities. Monitor patients for signs or symptoms of
neurologic toxicities for 4 weeks after infusion and treat promptly.

YESCARTA REMS: Because of the risk of CRS and neurologic
toxicities, Yescarta is available only through a restricted program
under a Risk Evaluation and Mitigation Strategy (REMS) called the
Yescarta REMS. The required components of the Yescarta REMS are:
Healthcare facilities that dispense and administer Yescarta must be
enrolled and comply with the REMS requirements. Certified healthcare
facilities must have on-site, immediate access to tocilizumab, and
ensure that a minimum of 2 doses of tocilizumab are available for each
patient for infusion within 2 hours after Yescarta infusion, if needed
for treatment of CRS. Certified healthcare facilities must ensure that
healthcare providers who prescribe, dispense or administer Yescarta are
trained about the management of CRS and neurologic toxicities. Further
information is available at www.YESCARTAREMS.com
or 1-844-454-KITE (5483).

HYPERSENSITIVITY REACTIONS: Allergic reactions may occur. Serious
hypersensitivity reactions including anaphylaxis may be due to dimethyl
sulfoxide (DMSO) or residual gentamicin in Yescarta.

SERIOUS INFECTIONS: Severe or life-threatening infections
occurred. Infections (all grades) occurred in 38% of patients, and in
23% with ≥ Grade 3. Grade 3 or higher infections with an unspecified
pathogen occurred in 16% of patients, bacterial infections in 9%, and
viral infections in 4%. Yescarta should not be administered to patients
with clinically significant active systemic infections. Monitor patients
for signs and symptoms of infection before and after Yescarta infusion
and treat appropriately. Administer prophylactic anti-microbials
according to local guidelines. Febrile neutropenia was observed in 36%
of patients and may be concurrent with CRS. In the event of febrile
neutropenia, evaluate for infection and manage with broad spectrum
antibiotics, fluids and other supportive care as medically indicated.
Hepatitis B virus (HBV) reactivation, in some cases resulting in
fulminant hepatitis, hepatic failure and death, can occur in patients
treated with drugs directed against B cells. Perform screening for HBV,
HCV, and HIV in accordance with clinical guidelines before collection of
cells for manufacturing.

PROLONGED CYTOPENIAS: Patients may exhibit cytopenias for several
weeks following lymphodepleting chemotherapy and Yescarta infusion.
Grade 3 or higher cytopenias not resolved by Day 30 following Yescarta
infusion occurred in 28% of patients and included thrombocytopenia
(18%), neutropenia (15%), and anemia (3%). Monitor blood counts after
Yescarta infusion.

HYPOGAMMAGLOBULINEMIA: B-cell aplasia and hypogammaglobulinemia
can occur. Hypogammaglobulinemia occurred in 15% of patients. Monitor
immunoglobulin levels after treatment and manage using infection
precautions, antibiotic prophylaxis and immunoglobulin replacement. The
safety of immunization with live viral vaccines during or following
Yescarta treatment has not been studied. Vaccination with live virus
vaccines is not recommended for at least 6 weeks prior to the start of
lymphodepleting chemotherapy, during Yescarta treatment, and until
immune recovery following treatment.

SECONDARY MALIGNANCIES: Patients may develop secondary
malignancies. Monitor life-long for secondary malignancies. In the event
that a secondary malignancy occurs, contact Kite at 1-844-454-KITE
(5483) to obtain instructions on patient samples to collect for testing.

EFFECTS ON ABILITY TO DRIVE AND USE MACHINES: Due to the
potential for neurologic events, including altered mental status or
seizures, patients are at risk for altered or decreased consciousness or
coordination in the 8 weeks following Yescarta infusion. Advise patients
to refrain from driving and engaging in hazardous occupations or
activities, such as operating heavy or potentially dangerous machinery,
during this initial period.

ADVERSE REACTIONS: The most common adverse reactions (incidence ≥
20%) include CRS, fever, hypotension, encephalopathy, tachycardia,
fatigue, headache, decreased appetite, chills, diarrhea, febrile
neutropenia, infections-pathogen unspecified, nausea, hypoxia, tremor,
cough, vomiting, dizziness, constipation, and cardiac arrhythmias.

About Kite

Kite, a Gilead Company, is a biopharmaceutical company based in Santa
Monica, California. Kite is engaged in the development of innovative
cancer immunotherapies. The company is focused on chimeric antigen
receptor and T cell receptor engineered cell therapies. For more
information on Kite, please visit www.kitepharma.com.

About Gilead Sciences

Gilead Sciences, Inc. is a research-based biopharmaceutical company that
discovers, develops and commercializes innovative medicines in areas of
unmet medical need. The company strives to transform and simplify care
for people with life-threatening illnesses around the world. Gilead has
operations in more than 35 countries worldwide, with headquarters
in Foster City, California. For more information on Gilead Sciences,
please visit the company’s website at www.gilead.com.

About Humanigen, Inc.

Humanigen, Inc. is developing its portfolio of Humaneered® monoclonal
antibodies to address cutting-edge CAR-T optimization and the need for
new oncology drugs that provide safer, better, and more effective cancer
therapies. Derived from the company’s Humaneered® platform, lenzilumab,
ifabotuzumab, and HGEN005 are monoclonal antibodies with first-in-class
mechanisms. Lenzilumab, which neutralizes human GM-CSF, is in
development as a potential biologic therapy to make CAR-T therapy safer
and more effective, as well as a potential treatment for hematologic
cancers. Ifabotuzumab, which targets the Eph type-A receptor 3 (EphA3),
is being explored as a potential treatment for a range of solid tumors,
as well as a backbone for a novel CAR-T construct, and a bispecific
antibody platform. HGEN005 which selectively targets the eosinophil
receptor EMR1 is being explored as a potential treatment for a range of
eosinophilic diseases including eosinophilic leukemia both as an
optimized naked antibody and as the backbone for a novel CAR-T
construct. For more information, visit www.humanigen.com.

Gilead Forward-Looking Statement

This press release includes forward-looking statements, within the
meaning of the Private Securities Litigation Reform Act of 1995 that are
subject to risks, uncertainties and other factors, including Kite’s
ability to complete the Phase 1/2 study of Yescarta in combination with
lenzilumab in patients with relapsed or refractory DLBCL in the
currently anticipated timelines, or at all. In addition, there is the
possibility of unfavorable results from clinical trials involving this
combination, Yescarta and other investigational CAR T therapies.
Further, it is possible that the parties may make a strategic decision
to discontinue development of the investigational combination of
Yescarta and lenzilumab. All statements other than statements of
historical fact are statements that could be deemed forward-looking
statements.  These risks, uncertainties and other factors could cause
actual results to differ materially from those referred to in the
forward-looking statements. The reader is cautioned not to rely on these
forward-looking statements. These and other risks are described in
detail in Gilead’s Quarterly Report on Form 10-Q for the quarter ended
March 31, 2019, as filed with the U.S. Securities and Exchange
Commission.  All forward-looking statements are based on information
currently available to Gilead and Kite, and Gilead and Kite assume no
obligation to update any such forward-looking statements.

Humanigen Forward-Looking Statement

This release contains forward-looking statements. Forward-looking
statements reflect management’s current knowledge, assumptions, judgment
and expectations regarding future performance or events. Although
management believes that the expectations reflected in such statements
are reasonable, they give no assurance that such expectations will prove
to be correct and you should be aware that actual events or results may
differ materially from those contained in the forward-looking
statements. Words such as “will,” “expect,” “intend,” “plan,”
“potential,” “possible,” “goals,” “accelerate,” “continue,” and similar
expressions identify forward-looking statements, including, without
limitation, statements regarding our expectations for future development
of lenzilumab to help CAR-T therapy reach its full potential.
Forward-looking statements are subject to a number of risks and
uncertainties including, but not limited to, the risks inherent in Black
Horse Capital and its affiliates owning more than 50% of our outstanding
common stock, including their ability to control the company; our lack
of profitability and need for additional capital to operate our business
as a going concern; the uncertainties inherent in the development and
launch of any new pharmaceutical product; the outcome of pending or
future litigation; and the various risks and uncertainties described in
the “Risk Factors” sections and elsewhere in the Company’s periodic and
other filings with the Securities and Exchange Commission.

All forward-looking statements are expressly qualified in their entirety
by this cautionary notice. You should not place undue reliance on any
forward-looking statements, which speak only as of the date of this
release. We undertake no obligation to revise or update any
forward-looking statements made in this press release to reflect events
or circumstances after the date hereof or to reflect new information or
the occurrence of unanticipated events, except as required by law.

U.S. Prescribing Information for Yescarta, including BOXED WARNING,
is available at www.kitepharma.com
and www.gilead.com.

Yescarta is a registered trademark of Gilead Sciences,
Inc., or its related companies.

1. Sterner, R., Sakemura, R., Cox, M., Yang, N., Khadka, R., Forsman,
   C.,… Kenderian, S. (2019). GM-CSF inhibition reduces cytokine release
   syndrome and neuroinflammation but enhances CAR-T cell function in
   xenografts. Blood : the official journal of the American Society of
   Hematology, 133:697-709. doi: https://doi.org/10.1182/blood-2018-10-881722

Contacts

Kite, A Gilead Company, Contacts:
Sung Lee, Investors
(650)
524-7792

Shant Salakian, Media
(424) 384-1841

Humanigen Contacts:
Al Palombo, Investors
(650) 243-3181
[email protected]

Chris Bowe, Media
(646) 662-7628
[email protected]