Inclusion Criteria:

- Phase 1: Histologically/cytologically confirmed lymphoproliferative malignancy.
Patients with Hodgkin lymphoma (HL) or non-HL are eligible, with exceptions per
exclusion criteria.

- Phase 2a: Histologically/cytologically confirmed HL, peripheral T-cell lymphoma
(PTCL), or B-cell lymphoma including Waldenström's macroglobulinemia, with exceptions
per exclusion criteria.

- Progression of disease (PD) after at least 1 prior treatment (any number of prior
therapies allowed). PD after last prior treatment and recovered from toxic effects
of prior therapy. Patients treated with an FDA-approved monoclonal antibody therapy
may be enrolled at any time after the therapy if they have PD.

- PTCL patients must have received single-agent pralatrexate as a prior therapy.

- Eastern Cooperative Oncology Group performance status ≤ 2.

- Adequate blood, liver and kidney function per laboratory tests.

- Has taken 1 mg daily oral folic acid for at least 7 days prior to planned start of
pralatrexate and received 1 mg vitamin B12 intramuscularly within 10 weeks of the
planned start of pralatrexate.

- Females of childbearing potential must practice a medically acceptable contraceptive
regimen from first dose until at least 30 days after last dose of pralatrexate and
have a negative serum pregnancy test within 14 days prior to the first day of study
treatment. Postmenopausal (defined as greater than 12 months since last menses) and
surgically sterilized females do not require this test.

- Males who are not surgically sterile must practice a medically acceptable
contraceptive regimen from first dose until at least 90 days after last dose of
pralatrexate.

- Give written informed consent.

Exclusion Criteria:

- Phase 1

1. B-cell: lymphoplasmacytic lymphoma (± Waldenström's macroglobulinemia); plasma
cell myeloma/plasmacytoma; hairy cell leukemia.

- Phase 2a

1. PTCL: precursor T/Natural Killer (NK) neoplasms, with the exception of blastic
NK lymphoma; T-cell prolymphocytic leukemia; T-cell large granular lymphocytic
leukemia; mycosis fungoides (MF), except transformed MF; Sézary syndrome;
primary cutaneous CD30+ disorders: Anaplastic large cell lymphoma and
lymphomatoid papulosis.

2. B-cell: plasma cell myeloma/plasmacytoma; hairy cell leukemia.

- Relapsed HL or diffuse large B-cell lymphoma patients who are candidates for high
dose therapy and autologous stem cell transplantation (SCT) and for whom it is a
standard curative option.

- Active concurrent malignancy (except non melanoma skin cancer or carcinoma in situ of
the cervix). If there is a history of prior malignancy, must be disease free for at
least 5 years.

- Congestive heart failure Class III/IV.

- Uncontrolled hypertension.

- Human immunodeficiency virus (HIV)- positive diagnosis with CD4 less than 100 or
detectable viral load within past 3 months and receiving anti-retroviral therapy.

- Hepatitis B or C virus with detectable viral load or immunological evidence of
chronic active disease or receiving/requiring antiviral therapy.

- Central nervous system disease.

- Undergone an allogeneic SCT.

- Patients with disease refractory to peripheral blood SCT, or who have relapsed less
than 100 days since an autologous or peripheral blood SCT.

- Active uncontrolled infection, underlying medical condition including unstable heart
disease, or other serious illness impairing the ability to receive protocol
treatment.

- Major surgery within 2 weeks of planned start of treatment.

- Receipt of any conventional chemotherapy or radiation therapy (encompassing greater
than 10% of bone marrow) within 4 weeks (6 weeks for nitrosoureas or mitomycin C)
prior to study treatment or planned use during the study.

- Receipt of systemic corticosteroids within 7 days of study treatment, unless on a
continuous dose of no more than 10 mg/day of prednisone for at least 1 month.

- Use of investigational drugs, biologics, or devices within 4 weeks prior to study
treatment or planned use during the study.

- Received a monoclonal antibody within 3 months without evidence of PD.

- Previous exposure to pralatrexate and/or gemcitabine if discontinued due to
treatment-related toxicity.